Margarine 12

12Margarine ProcessingPlants and Equipment

Klaus A. Alexandersen

When designing margarine processing plants and choosing the equipment to be

installed, a wide range of considerations have to be made with regard to issues

like actual processing, hygiene, sanitation, and efficiency.

In margarine production, oils and fats usually are considered to be the most

important raw materials used, as oils and fats are significant in relation to

the characteristics of the finished margarine. The type of oils or fats used

has considerable influence on the crystallization characteristics during marga-

rine processing, which has to be considered when choosing the equipment

involved in the margarine processing line. The criteria involved in choosing

this equipment are to a certain extent based on knowledge about product

characteristics, polymorphism, and crystal structure of margarine and related

products.

In this chapter, crystallization of oil and fat products, margarine processing

equipment and packaging methods, processing methods, and specific process flows

are discussed. Various oil types exhibiting interesting crystallization habits are

reviewed along with certain specialized margarine or fat products. Storage of

finished products as well as production quality control and hygiene will also be

covered.

Baileys Industrial Oil and Fat Products, Sixth Edition, Six Volume Set.Edited by Fereidoon Shahidi. Copyright # 2005 John Wiley & Sons, Inc.

459

1. CRYSTALLIZATION OF OIL AND FAT PRODUCTS

1.1. Product Characteristics

The rheological characteristics of finished margarines are expressed in terms such

as consistency, texture, plasticity, hardness, structure, and spreadability (1).

These characteristics are related to a number of variable factors. These are

temperature, concentration of the disperse phase or solid fat content, crystal size,

crystal size distribution, crystal shape, interparticle forces of van der Waals type

and mechanical treatment (2).

The two dominating factors are the amount of solid triglycerides (or solid fat

index) and the processing conditions during production (3). Formulation or choice

of oil blend allows control of the solid content, which, for identical processing

conditions, is directly related to the consistency and type of crystalline structure

formed (35). Processing conditions (rate and degree of cooling, mechanical

working, final product temperature, etc.) regulate the type of crystals formed and

the morphology and extent of intertwining of the solid structure that holds the

liquid oil (6).

The term morphology is used to denote the general relation of the physical

behavior and performance of fats and oils to their crystal structure and the molecu-

lar configuration of their triglyceride components (7).

The curve describing the relationship between the solid fat content of a fat and

its hardness is not a straight line. Hardness decreases sharply when solid fat content

goes below a certain value at which the material loses some of the characteristic

plastic properties (2). Haighton (3, 8) has reported the hardness of margarine in

terms of yield value to have a strong correlation to the solid content under constant

processing conditions, as shown in Figure 1.

1.2. Polymorphism and Crystal Structure

It has been reported extensively that fats solidify in more than one crystalline type

(223). Triglycerides exhibit three main crystal typesa; b0, and bwith increas-ing degrees of stability and melting point. The molecular conformations and

packings in the crystal of each polymorph have been reported. In the a form, thefatty acid chain axes of the triglyceride are randomly oriented and the a formreveals a freedom of molecular motion with the most loosely packed hexagonal

subcell structure.

The b0 form and the b form are of an extended chain conformation with ortho-rhombic and triclinic subcell structures, respectively. In the b0 form alternating fattyacid chain axes are oppositely oriented, whereas in the b form all fatty acid chainaxes are oriented in one way (9, 10).

Crystals of the a form are fragile, transparent platelets approximately 5 mm insize. They are extremely transitory and require quite low temperatures to exist.

b0 crystals are tiny needles seldom more than 1 mm in length. b crystals are large

460 MARGARINE PROCESSING PLANTS AND EQUIPMENT

and coarse, approximately 2550 mm in length and can grow to over 100 mm duringextended periods of product storage. The b form is responsible for product qualityfailure in sandy and grainy margarines (7). In severe cases this can lead to

separation of the oil usually described by the term oiling out. Storage temperature

that is too high, inadequate oil blend formulation, or process conditions promote

this product failure.

In the manufacture of margarine, the emulsion is processed in a scraped-surface

heat exchanger that must supercool the melted fat quickly in order to form as many

crystal nuclei as possible (11).

The fat is believed to first crystallize in the a form, which is transformed more orless rapidly to the b0 form depending on the crystal habit of the fat, rate of cooling,and the amount of mechanical work applied (5, 7, 12, 13).

b0 is the crystal form desired in margarines as it promotes plasticity (4, 5, 13).The b0 crystal form tends to structure as a fine three-dimensional network capable

Figure 1. Hardness of margarine vs. percentage solid in fat (3). Courtesy of J. Amer. Oil Chem.

Soc.

CRYSTALLIZATION OF OIL AND FAT PRODUCTS 461

fruta planta

of immobilizing a large amount of liquid oil (6). Large b crystals do not tend togive a three-dimensional structure.

Both Wiedermann (4) and Thomas (5) have grouped various oils and fats accord-

ing to their crystal habits. As an example, soybean, sunflower seed, corn, coconut,

and peanut oils show a b tendency. Cottonseed oil, palm oil, tallow, and butter oilhave a b0 tendency. Oil blend formulation has a significant influence on the crystalform attained by a margarine or shortening. The suitability of a fat or oil for

margarine formulation is very much dependent on the crystal size present, amount,

and habit of these crystals (13). Incorporation of a higher melting b0 tending oil to abasestock can induce the crystallization of the entire fat into a stable b0 form (5).The effects of such formulation practice and processing conditions have been

studied extensively by Rivarola et al. (6) for blends of hydrogenated sunflower

seed oil and cottonseed oil. For strong b tending hydrogenated sunflower seedoil, it was found that with increasing cooling rate, the tendency to crystallize in

the b0 form increased. For blends of hydrogenated sunflower seed oil and strongb0 tending hydrogenated cottonseed oil it was concluded that even at quick coolingrates, small quantities of the b form are formed.

In certain margarines formulated mainly on hydrogenated oils, such as sunflower

seed oil and canola oil, with very strong b tendency, the problem of sandiness canbe pronounced. Addition of crystal-modifying agents or crystal inhibitors to such

margarines can retard the development of sandiness by delaying the transformation

from the unstable a form to the stable b form. The addition of sorbitan estersstabilizes the intermediate b0 form and helps prevent the formation of the b form(15, 16). Sorbitan tristearate is effective as a crystal inhibitor in margarines. It is

assumed that sorbitan tristearate can be accommodated by the b0 crystal networkof the triglycerides and by stearic hindrance prevent the formation of the more

densely packed b crystal form (17, 18).In margarine with a good consistency, the fat crystals have formed a three-

dimensional network consisting of primary and secondary bonds. The crystals may

vary in shape and appearance in the form of small needles or platelets with lengths

ranging from less then 0.1 to 20 mm or more (3, 6). They do not behave as indi-vidual particles and can grow together, forming a strong network (primary bonds).

They may also show a tendency to agglomerate, forming tiny porous crystal

clusters with considerable fewer contact points (secondary bonds) (3). As a result

of this and depending on the resulting crystal form obtained, branched and inter-

twining long chains are formed (6). These chains are responsible for forming

the three-dimensional network. The primary bonds are strong and are not readily

reestablished when broken by mechanical work. Secondary bonds are weak and

readily reestablished when broken by application of mechanical work. As men-

tioned earlier, processing conditions involving fast cooling rates and application

of a certain amount of mechanical work tend to produce margarines with a better

stability and consistency. It is generally accepted that a larger amount of primary

bonds are established if margarine is allowed to crystallize without sufficient degree

of mechanical work. This results in a product exhibiting excessive posthardening

and a hard and brittle texture (19). Due to this, it is advantageous to crystallize


fruta planta

the product as much as possible in the scraped-surface heat exchanger to achieve

the desired spreadability or consistency.

1.3. Palm Oil

Crystallization and processing of palm oil with satisfactory results in a scraped-

surface heat exchanger line for margarine and shortening requires some attention

due to the slow crystallization phenomena observed in palm oil.

The polymorphism, crystallization, formulation, and processing of palm oil has

been commented upon and studied extensively (2025, 2634). The slow crystal-

lization of palm oil and the subsequent posthardening phenomenon and product

graininess is a drawback in products formulated with high palm oil contents

and could be a limiting factor to its use (24, 25). It has been shown that the rate-

determining step in the crystal growth mechanism of triglycerides is the orientation

of molecules at the crystal faces (20). In palm oil the a-polymorph transformationto the b0 (i.e., the a lifetime) is unusually long, which is apparently due to thehigh level of diglycerides present (approximately 6%) (20, 21). The problem of

posthardening in product formulated with high palm oil contents can be influenced

by choice of proper processing conditions and storage time (2123).

Lefebvre (35) hypothesized that crystals, in general, are formed before or early

in the worker unit (B unit) (see Section 2.3), when a low flow rate is used in a

scraped-surface heat exchanger. The important slow processing of the product

leads to a fine crystallization and the destruction of the intercrystal bonds of the

primary type. With a higher flow rate, crystals appear late in the worker unit and

partially during packaging. Crystallization is then coarser and intercrystal bonds

are only slightly damaged, all of which is less favorable.

This hypothesis relates very well with the observations made by Oh et al. (22)

during pilot-plant-scale crystallization and processing of palm oil in a scraped-

surface heat exchanger line for margarine and shortening, as shown in Figure 2.

Palm oil from the same batch was processed with flow rates A and B of, respec-

tively, 28 kg/h and 55 kg/h. Different flow rates result in different retention times

for products A and B in the coolers and the worker unit. Product outlet temperatures

from cooler II of, respectively, 12C and 14C (54F and 57F) were observed.The outlet temperature from the worker unit were, respectively, 1920C (6668F) and 2021C (6870F).

Refrigerant temperatures remained constant for both flow rates. Product A

was found to have sufficient time to be more uniformly stabilized before leaving

the process line. Product B was found to have attained insufficient time to be

uniformly stabilized and resulted in a finished product in the quasi-equilibrium

state. Crystal growth in product A was not substantial during 10 days storage at

20C (68F), whereas the crystal growth for product B was significant underthe same storage conditions. It was concluded that better processing conditions

may overcome the problem of slow crystallization of palm oil and also avoid the

effect of posthardening during storage. Different compositions of palm oil and palm

oil fractions give rise to different crystallization behaviors. Hydrogenated palm oil


fruta planta

has the highest stability in the b0 crystal form followed by palm oil and then palmstearin.

The preceding observations relate well with observations in industrial-scale

scraped-surface heat exchanger processing lines.

In industrial-scale processing lines, it has been found to be advantageous to

process palm-oil-based industrial margarines with an additional worker unit

installed between the cooling cylinders as shown in Figure 3 (26). This increases

the products retention time in the processing line and allows a slight increase in the

flow rate without compromising the product quality.

Generally, the recommended flow rate for palm-oil-based industrial margarines

is approximately 60% of the nominal capacity of a scraped-surface heat exchanger

process line for industrial margarine (27); for example, a scraped-surface heat

exchanger with a nominal capacity of 3000 kg/h for oil blends based on oils such

as soybean oil or cottonseed oil will, for oil blends based on palm oil, have a

capacity of approximately 1800 kg/h.

In connection with crystallization of palm-oil-based products it should be noted

that the tempering practice for industrial margarines and shortening at 26.7C(80F) was designed especially for hydrogenated oils. This tempering proceduretends to generate lower solid fat content at temperatures below 26.7C (80F)and raise it above 26.7C (80F). It is generally unsuitable for palm oil, palm-kerneloil, and coconut oil (21).

Figure 2. Schematic diagram of pilot plant (22). Courtesy of The Palm Oil Research Institute of

Malaysia.


fruta planta

1.4. Canola Oil and Sunflower Seed Oil

We have noted earlier that the crystallization of strongly b tending sunflower seedoil blends can be influenced favorably toward the b0 polymorph form by addition ofa high melting hardstock of the hydrogenated cottonseed oil (6) as well as by addi-

tion of sorbitan tristearate (17, 18). It should be noted for the formulation and crys-

tallization of margarines based on sunflower seed oil blend that interesterification of

oil blends is a possible route to minimize posthardening. It is possible to produce

table margarine with good consistency and a linoleic acid content of 36% as well as

a trans-isomeric fatty acid content of less then 2% based on an oil blend prepared

by interesterification. Interesterification of a blend consisting of 60% sunflower

seed oil, 15% coconut oil, and 25% hydrogenated sunflower seed oil [melting point

70.7C (159F)] and an iodine value (IV) of 8.5 can achieve this.Interesterification has been reported to change the crystallization tendencies of

oil blends in such a way that the crystal size in certain interesterified oil blends is

smaller than in the similar noninteresterified oil blends (3639). List et al. (40)

found that interesterification of oil blends made from fully hydrogenated soybean

oil and soybean oil affects the polymorphic transition from the undesirable b formto the desirable b0 form thus avoiding graininess in finished margarine products.Interesterification of blends of palm oil fractions is also a possibility in margarine

formulation producing margarines with very low or zero trans fatty acid contents

Figure 3. Schematic diagram of industrial source plant.


(41, 42). With todays health conscious discussions in the media and the use of

transisomeric fatty acid content in margarines as a marketing parameter, the inter-

esterification of oil blends may possibly gain some momentum in the future.

It is well documented that hydrogenated canola oil has a tendency to crystallize

in the b polymorphic form due to its triglyceride homogeneity (it has about 95%of 18-carbon fatty acids) (43). Crystallization of b tending canola oil blends(low-eururic-acid rapeseed oil) can be influenced by addition of an oil with b0

tending crystallization of different origin. When processing canola-oil-blend-based

margarines for tub or stick packaging, the industry follows a different formula-

tion principle than for sunflower seed oil blends, which are usually used for soft

margarines with high linoleic acid contents. Canola oil constitutes approximately

42% of all vegetable oils consumed in the margarine production in Canada (44),

whereas soybean oil constitutes the majority of all oils supplied for the production

of margarine in the United States (45).

Canola oil contains 5% palmitic acid compared to 11% for soybean oil. Palm oil

contains high levels of palmitic acid, approximately 44%, and it has been found that

the addition of palm oil to canola-oil-based oil blends for margarine production has

a beneficial effect on their polymorphic stability (30). When palm oil is mixed with

canola oil, the homogeneity of the fatty acid chain length is reduced, which pro-

motes b0 crystalline stability (43). Based on the solid fat content found in stickmargarine in North America, it is advantageous to manufacture margarine from

canola oil by incorporating palm oil at a level of at least 15%, after hydrogenation

of canola oil, or at a level of 10%, before hydrogenation of canola oil. This greatly

delays the polymorphic transition from the b0 to the b form (43, 46, 47). Theamount and point of addition can affect the transition to the b polymorph as hydro-genation changes the physical properties of an oil blend (46).

The high content of diglycerides (about 6%) in palm oil and the b0 stabilizingeffect of diglycerides probably do not have any significant influence on the poly-

morphic behavior of canola oil blends with palm oil levels as above. The diglycer-

ide content in canola oil blends is only raised slightly by addition of palm oil in the

above levels (46).

It has been found that the b0 stabilizing effect increased with the level of addedpalm oil and that this stabilizing effect is most likely due to the decrease in fatty

acid homogeneity and, thus, increased triglyceride diversity (43, 46). This is attri-

buted to the increased range of fatty acid chain lengths, which in turn increases the

irregularity in the crystal network. Increased irregularity in the crystal network

increases the polymorphic stability (46).

A new type of canola oil containing high levels of palmitic acid possesses better

b0 stability in the hydrogenated form (30, 46). The stabilizing effect of palmiticacid, mentioned by Wiedermann (4), is related to its level in the solid fat fraction,

which is increased by addition of palm oil or when the palm oil is partially hydro-

genated (46). In general, the more diverse the triglyceride structure of the highest

melting portion of the fat, the lower the b forming tendency (48).To illustrate this, the triglyceride composition of some fully hydrogenated oils

are indicated in Table 1.


In Table 1, the most b0 stable fat is palm oil hard fat. This may be explained byits unique composition, and its balanced C48C54 triglyceride content with an

equally balanced C50C52 content (49).

In accordance with the above, it has been found that slightly hydrogenated palm

oil delayed polymorphic transition from b0 to b considerably, compared to no palmoil addition (43).

Stick margarine of good quality and melting point, 35C (95F), based on acanola oil blend with palm oil addition, can be produced in a scraped-surface heat

exchanger line for margarine, according to the flow outline in Figure 4. A reduced

flow rate of approximately 85%, compared to the nominal capacity of the scraped-

surface heat exchanger (A unit) (see Section 2.2), is recommended. It should also

be noted that the intermediate worker unit (B unit) (see Section 2.3), with variable-

speed drive inserted between the cooling cylinders, should have a relative volume

of approximately one third of the volume of the intermediate worker unit indicated

in Figure 3, based on a given flow rate and heat exchange area (50).

1.5. Specific Heat and Heat of Fusion

In the solid state, the specific heat of oils and fats shows little change as molecular

weight varies. An increase in specific heat can be observed with increased unsatura-

tion. In the liquid state, specific heat increases slightly with molecular weight but

decreases slightly with less unsaturation. In general, there is little variation among

natural oils and fats (21).

TABLE 1. Percent (%) Triglyceride Composition and Mono- and Diglyceride Content

of Fully Hydrogenated Oils (%).

Hard Fats

Carbon Rapeseed

Number Soybean Beef Fata Rapeseed Blend Cottonseed Palm

44 0.2

46 1.4 0.1 0.5

48 0.2 7.5 3.4 0.9 6.4

50 3.3 21.0 1.6 8.8 13.6 40.0

52 27.6 44.9 11.6 15.2 43.5 41.9

54 66.7 24.5 28.3 25.9 40.5 10.7

56 1.7 0.4 6.7 6.2 1.3 0.4

58 0.5 6.8 7.2

60 12.3 9.0

62 31.9 23.6

64 0.8 0.8

Monto 0.4 0.1 0.5 0.5 0.3 0.9

Di 3.6 2.0 3.7 4.4 5.8 8.2

aGlycerides contain odd-numbered and branched fatty acids.

Reprinted from Ref. 49, with permission.


The specific heats of liquid oils and fats, including palm oil, palm kernel oil, and

coconut oil, may be taken as (21).

Cpkcal=kg 0:47 0:00073 T ;

where T is temperature in C (1 Btu/lb 0.252 kcal/kg).A specific heat of 0.514 kcal/kg/C for the fat phase of a retail margarine with

82% fat content and 0.607 kcal/kg/C for the same margarine has been reported (19).It is difficult to determine the latent crystallization heat in oil blends for

margarine production due to their complexity.

The heat of fusion normally increases with bigger chain lengths and decreasing

unsaturation in the triglycerides. Blends of triglycerides have less latent heat of

crystallization than the similar nonblended triglycerides (19).

Timms (21) has heat of fusion to 17.722.3 kcal/kg for milkfat, 2431 kcal/kg

for fully hardened milkfat, 2629 kcal/kg for cocoa butter in the b0 polymorph,22.6 kcal/kg for refined, bleached, and deodorized (RBD) palm oil, 29.7 kcal/kg

for RBD palm kernel oil, 26.0 kcal/kg for RBD coconut oil, 31.6 kcal/kg for

fully hardened palm kernel oil, and 31.2 kcal/kg for fully hardened coconut oil.

The heat of fusion is an empirical physical property dependent on the thermal

history or tempering of the oil.

Calvelo (19) has reported the total heat of crystallization (Jc) for a specific retail

margarine with 82% fat content to be 33.4 kcal/kg.

Figure 4. Schematic diagram stick (table) margarine plant.


2. PROCESSING EQUIPMENT FOR MARGARINEAND RELATED FAT PRODUCTS

Choice of equipment for the processing line is very important for the production of

margarines. For each piece of equipment in the production line, special design

features have to be considered for various margarine types to ensure that the

complete processing line has all the necessary capabilities.

Besides the necessary emulsion preparation equipment (see Sections 4.14.3)

such as process tanks, plate heat exchangers, and centrifugal pumps, the essential

equipment for production of margarines is discussed in the following sections.

2.1. High-Pressure Feed Pumps

The margarine emulsion is usually fed from a holding tank to the scraped-surface

heat exchanger (A unit) by a high-pressure positive-displacement pump of the

plunger or piston type with product contact parts in 316 stainless steel. Pumps

with ceramic pistons are available for special applications. Normally, pumps with

two or three plungers or pistons are standard in order to minimize discharge

pressure pulsations in the process line. A high-pressure piston pump for margarine

production is illustrated in Figure 5.

To further minimize possible pressure pulsation, the pumps can be installed

together with a pulsation dampener mounted at the discharge. Pulsation dampeners

are air pressurized or spring loaded to ensure a smoother product flow in the process

line. Slow rotational speed of the pumps crankshaft also helps to minimize pressure

pulsation.

The high-pressure pumps are normally supplied with a pressure relief valve and

associated product piping to protect the scraped-surface heat exchanger equipment

downstream and the pump itself, should a blockage of the production line occur.

A filter is normally installed in the suction line to the high-pressure pump to

protect the pump and the hard chromium-plated scraped-surface heat exchanger

cylinder from any foreign matter in the margarine emulsion.

Depending on the designed maximum product pressure of the downstream

scraped-surface heat exchanger and the various types of margarine produced,

high-pressure positive-displacement pumps with maximum discharge pressures of

40 bars (about 600 psi), 70 bars (about 1030 psi), or 120 bars (about 1800 psi) are

normally installed in the process line.

Production of industrial margarine for semiliquid filling does not normally

generate product line pressures as high as, for example, puff pastry margarine.

Gear pumps are normally installed as an alternative to high-pressure positive-

displacement pumps in the production of industrial margarine or shortening for

semiliquid filling (26, 51). Gear pumps for this application normally can deliver

a maximum discharge pressure of 2633 bars (about 390500 psi). The drawback

for the application of gear pumps in margarine processing is that this type of pump

tends to slip at higher discharge pressures (52).

PROCESSING EQUIPMENT FOR MARGARINE 469

2.2. High-Pressure Scraped-Surface Heat Exchanger

Scraped-surface heat exchanger equipment, specifically designed for margarine

production, is available from Cherry-Burrell Votator Division of Louisville,

Kentucky, United States, Crown Chemtech Ltd. of Reading, U.K., Gerstenberg &

Agger A/S of Copenhagen, Denmark, and Schroeder & Co. (Tetra-Laval owned) of

Luebeck, Germany, under the respective trademarks Votator, Chemetator, Perfector,

and Kombinator.

The scraped-surface heat exchanger (A unit) is the centerpiece of equipment of

the margarine processing line, where initial cooling, supercooling, and subsequent

induced nucleation and crystallization take place (3, 53). The A unit has to have a

high degree of flexibility with regard to variation of process conditions for different

product types and formulations (51, 53).

Figure 5. High-pressure piston pump for margarine production. Courtesy of Schroeder & Co.,

Luebeck, Germany.


The scraped-surface heat exchanger normally consists of one or more horizontal

heat transfer cylinder assemblies. The cooling cylinder of a cylinder assembly is

usually made from commercially pure nickel or steel, ensuring high heat transfer

coefficients. The cooling cylinder is surrounded by an insulated outer jacket con-

taining refrigerant (normally ammonia or Freon 22). The inside hard chromium-

plated surface of the cooling cylinder is continuously scraped clean during

operation by a rotating shaft mounted with free-floating blades. The blades are

thrust against the cylinder wall mainly by the centrifugal force resulting from the

high rotational speed of the shaft. The annular gap between the cylinder wall and

the shaft has been reported to be in ranges from 3 to 22 mm (52), but a more typical

range is 517 mm (3, 5154).

When margarine emulsion passes through the space between the shaft and

cylinder wall, a thin crystallized product film is constantly and very rapidly scraped

off the cylinder wall and remixed with warmer product because of the scraping

action of the blades and the shafts high rotation speed. This causes rapid crystal

nucleation, further emulsification of the product, very high overall heat transfer

coefficients, and a homogeneous cooling of the margarine emulsion under precise

temperature control of the product being crystallized (5355).

The rotational speeds of shafts normally range from 300 to 700 rpm (5153)

and shafts are normally mounted with two, four, or six rows of blades (53).

The blades are fixed to the shafts by specially designed pins and are movable

at their fixing points. Figure 6 illustrates the design and operation of a scraped-

surface heat exchanger based on a longitudinal view of the A unit and a cross-

sectional view of the cooling assembly. The shaft is mounted with four rows of

blades in a staggered configuration. The annular gap in this situation varies from

9 to 17 mm.

In the crystallizing product, there is a rapid increase in the solid content during

the passage through the cooling cylinder. Also, the viscosity of the product

increases accordingly with the temperature drop. At a certain point during this

process, a critical shaft speed is reached. Beyond this speed, no additional mixing

is obtained, and the power input required to rotate the shaft at a higher speed will

more than offset any heat transfer benefits resulting from more frequent scraping of

the cylinder wall (54, 55).

In order to prevent buildup of crystallizing product on the shaft, warm water

is normally circulated through the shaft to ensure a clean shaft surface at all times

(5154). The warm water is normally pumped into the shaft at a point near the

thrust/axial bearing assembly and exits close to the water inlet point based on the

inside construction of the shaft (52). The water circulation facility is also beneficial

after a temporary production stoppage, as the warm water helps to melt solidified

product and, thus, facilitates the restart of the A unit.

Energy Balance. The above-mentioned temperature drop, crystal nucleation, and

partial crystallization of the product during the passage through the A unit involve

an overall energy balance including specific and latent heat of the product as well as

other energy source inside the equipment. The power input through the blade shaft

is transferred to the product and the cylinder wall as heat (Qm). A small amount of


Figure 6. Scraped-surface heat exchanger. Courtesy of Crown Chemtech U.S.A., a division of Crown Iron Works Co., Minneapolis, Minnesota.

472

heat is also added to the process through the warm water circulation inside the

shaft (Qw).

According to this, the energy in form of heat in the A unit can be expressed as

follows (19):

Qt FCpT1 T2 FJcW2Y Qm Qw; 1

where F is the flow rate, Cp the products specific heat, T1 the emulsions inlet

temperature, T2 the product exit temperature, Jc the latent heat of crystallization

in the fat, W2 the solid fat content at the exit from the A unit, and Y the fat content

of the margarine emulsion.

In a stationary condition, the heat Qt will presumably be transferred through the

cylinder wall at an ammonia evaporation temperature of Tf , which makes it possible

to define the heat transfer coefficient U as

Qt UAT ln; 2

where A is the heat transfer area and T ln is a logarithmic value defined as

T ln T1 lnT1=T2T2; 3

where T1 T1 Tf and T2 T2 Tf .If the product at the exit from the A unit has a solid fat content of W2 at tempe-

rature T2 and is left to crystallize under stationary conditions, the degree of super-

cooling will be reduced with time, as the crystallization continues until a certain

temperature Ta has been reached. Based on this we have

CpTa T2 JcYWa W2; 4

where Wa is the solid fat content at temperature Ta. Based on sufficient time to

achieve a stable situation, Wa can be determined from the solid fat curve in the pro-

duct at temperature Ta.

From formula (4) the solid fat content at the exit of the A unit, W2, can be

calculated as follows:

W2 Wa CpTJcY

; 5

where T Ta T2.Formulas (1), (2), and (5) make it possible to relate process variables such as

the flow rate F, the emulsion temperature T1, and the ammonia evaporation tempe-

rature Tf with parameters contributing to the consistency of the margarine such as

the solid fat content at the exit of the A unit W2.

As the crystallization of a fat product demands both a rapid temperature

drop and time for crystal nucleation and crystal growth, sufficient retention


time for the product in the A unit is required. The retention time can be calculated

from

Tr V=F; 6

where F is the product flow rate and V is the product volume in the A unit.

Shaft Design. The high viscosity margarine products exhibit during processing

in the A unit increases the significance of factors such as flow rate, shaft rotation

speed, turbulent flow conditions in relation to shaft design, blade configuration, and

annular gap between the shaft and cylinder wall (51). This is due to the viscositys

influence on flow properties, created turbulence, increased effect of mechanical

work, and obtained mixing and heat transfer.

Several shaft or cylinder designs are available today in A units for margarine

processing. The A units can be grouped according to whether they are mounted

with eccentric shafts, oval shafts, sectioned shafts, or oval tubes.

Eccentric shafts have been in wide use in the past and were developed by the

Votator Division of Louisville, Kentucky, and are claimed to provide more intensive

cooling for high-melting bakery margarine as well as a certain amount of working

and compression action similar to that given by the Complector of the older, open-

chill drum system (52) (see Section 5.2).

Figure 7. Votator scraped-surface heat exchanger unit. Courtesy of Cherry-Burrell Votator

Division, Louisville, Ky.


Figure 7 shows a new, all stainless steel Votator A unit complete with high-

pressure feed pump and worker unit for production of industrial margarines and

shortenings.

In the literature, one can find theoretical and practical studies relating to heat

transfer conditions in scraped-surface heat exchangers (19, 54), which cover factors

such as specific weight, specific heat, latent heat of crystallization, dry matter con-

tent, retention time, and overall heat transfer conditions.

A review of some of the fluid mechanics and heat transfer aspects of scraped-

surface heat exchangers currently available for margarine processing has been

given by N. Hall Taylor (56). A summary by N. Hall Taylor outlining the important

physical phenomena occurring under different circumstances in the A units is given

in the following discussion.

Heat Transfer and Viscous Dissipation for Newtonian Fluids. Because the gap

width is small relative to the shaft radius, the annular space can be represented

on the basis of a two-dimensional flow model. This is illustrated in Figure 8.

Figure 8 indicates the important action of the scraper blade. Removal of material

at the front allows fresh warm material to flow down the back of the blade to

be brought into contact with the cold surface. Two things then happen. First, the

material adjacent to the surface is slowed down to develop a velocity profile.

Second, the material starts to transfer heat into the wall.

This is a transient fluid flow and heat transfer problem. Figure 9 illustrates the

growth of these layers adjacent to the wall as seen from a coordinate system travel-

ing with the blade.

In Figure 9, the upper line represents the viscous layer, which shows the progres-

sive development of the linear velocity profile. The thickness at any position rela-

tive to the blade is given approximately as

dn 2 nxV

1=2;

where n is the kinematic viscosity. The material outside this viscous layer continuesto travel at the rotational velocity V.

Figure 8. Fluid movement in the proximity of the blade (56). Courtesy of N. Hall Taylor, Crown

Chemtech Ltd., Reading, United Kingdom.


The inner line in Figure 9 represents the corresponding thermal layer and shows

the development of the thermal gradient. Again the material outside this layer

remains at a constant temperature above the wall temperatures (i.e., y0 yw). Thethickness of the thermal layers (dT ) is given by

dT 2 axV

1=2;

where a is the thermal diffusivity.Thus the ratio of the thickness of the two layers at any position is solely related

to the Prandtl number of the material:

dndT

na

1=2 Pr1=2:

For foodstuffs under low shear conditions, the Prandtl number is large, i.e., the

viscous layer is much thicker than the thermal layer.

Within the viscous layer, all the viscous dissipation is taking place. The scale of

viscous heat generation/unit volume (p) at any point is given by

p m dudy

2;

where du=dy is the velocity gradient.It can be shown that within the viscous layer:

p rV2

4t;

or in coordinates relative to the blade:

p rV3

4x:

Figure 9. Velocity profile behind the blade (56). Courtesy of N. Hall Taylor, Crown Chemtech

Ltd., Reading, United Kingdom.


This result is only true provided the thickness of the viscous layer is less than the

gap width (H); i.e., dn < H.By integrating the viscous dissipation terms over the volume of the viscous layer,

one can derive an equivalent heat flow that has to be removed in addition to any

cooling that takes place. This is given by

qn rV3 nLV

1=2;

where L is the distance behind the blade at which the viscous boundary layer is

destroyed. This can either be due to the next blade (so that L is the distance between

the blades) or because of some turbulent motion in the liquid. The cause of such

turbulent action will be discussed in detail later.

The heat transferred from the thermal layer to the wall can also be estimated and

averaged over the mixing length. This gives

qT ky VaL 1=2

:

Thus, increasing the rotational velocity will improve the rate of heat transfer

(proportional to V1=2). However, at the same time the heat that has to be removed

from viscous dissipation is increasing (proportional to V5=2).

The net cooling flux is

qc qT qV :

This indicates that for a given material there will be an optimum velocity at which

the greatest cooling is achieved. It also suggests that under certain conditions

qT qV and no net cooling is achieved.This will occur if

V2 > Cpy Pr1=2

or

V2 > Cpyk

Cpm

1=2:

The velocity at which this takes place will decrease as the viscosity increases. In a

margarine process the most critical section is in the final scraped-surface heat

exchanger (SSHE) and then toward the exit end. Here there is the greatest viscosity

(highest Pr) and also the smallest temperature difference between the wall and the

material (y).In most cases this critical velocity is well above the maximum operating velocity

of the SSHE.


Non-Newtonian Fluids. Most foodstuffs and margarines are non-Newtonian fluids.

This means that the effective viscosity varies with the shear applied to the material.

A useful representation of this behavior is as follows:

n n0 g0g K

;

where g is the shear rate, essentially equal to the velocity gradient; n0 is a referenceviscosity at the reference shear rate g0 s1; and k is a constant typically in therange 0.60.7. It should also be remembered that viscosity is generally strongly

dependent on temperature. This can typically be represented by

n nR yyR

n;

where nR is a reference viscosity at temperature yR and n is a constant in therange 23.

The influence of shear on viscosity has a very significant influence upon the rate

of development of the viscous boundary layer.

The shear in the viscous layer is given by

g Vdn

:

Thus, just behind the blade, the shear will be very high (since dn is very small),and this means that the effective viscosity will be low. Consequently, the layer will

move away from the wall more gradually than in the Newtonian fluid case.

A simplified equation for the thickness of the viscous layer for non-Newtonian

fluid is

dn dn0dn0g0

V

k=2k;

where

dn0 2n0xV

1=2:

The influence of the shear factor can be seen from the following table, which

shows the derived thickness (dn) as a function of dn0 for a velocity V of 2 m/s,equivalent to 300 rpm:

dn0 dn

1 0.02

2 0.06

4 0.18

8 0.50

16 1.41


This illustrates that the viscous layer is an order of magnitude smaller for the non-

Newtonian material when compared to a corresponding Newtonian material.

The thermal diffusion process, however, is not affected by the shear and so the

same equations as before apply. Thus, the thickness of the thermal layer becomes

closer to that of the viscous layer.

This analysis indicates that, for high-melting-point margarines, there is likely to

be a very thin layer close to the cooling surface in which a linear profile is devel-

oped. This is a region of high shear, which effectively lowers the viscosity within

this region. Outside this layer the material is moving uniformly with the rotating

shaft. This condition is often referred to as mass rotation.

There is, however, a number of instabilities that induce vortices, and these can

delay the onset of the mass rotation condition. The next section will discuss the

cause of these instabilities.

Flow Instabilities. For clarity, these instabilities will be discussed in terms of

Newtonian fluids, although similar, more complicated behavior will occur with

non-Newtonian fluids.

1. Instability behind the blade. The flow situation is equivalent to the analysis

of the transition from laminar to turbulent flow along a plate parallel to the

direction of flow and is shown in Figure 10. Instability is predicted to start at

Reynolds numbers greater than 580, although observable disturbances need a

higher value, say 1000.

Thus this type of disturbance will occur when

Re Vxn

> 1000:

On the basis of the earlier discussion, this implies a mixing length (L) of

L 1000nV

:

For water n 105 and so if V 2 m/s, L 5 mm. For an oil of 1000 cP, Lwill be about 5 m, in which case this instability will not be observed since the

distance to the next blade is only 0.2 m.

Figure 10. Instability behind the blade (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd.,

Reading, United Kingdom.


2. Instability within the annular space. The rotation of the fluid in the annular

space means that a centrifugal pressure gradient exists across the gap, the

higher pressure being at the wall. This pressure gradient is given by

dp

dr rV

2

r:

Ignoring the velocity gradients, this implies a pressure difference across

the gap of

p rV2 HR;

where R is the shaft radius.

For our standard SSHE, H 16 mm and R 61 mm so that at 300 rpmp is 0.01 bar, with the pressure at the cylinder wall being slightly higherthan at the shaft surface.

Although the pressure difference seems small compared to the local operat-

ing pressure of say 5070 bars, it is still capable of inducing a circulation

pattern. Thus, by Bernoullis equation, this pressure difference can accelerate

the liquid (ignoring viscous effects) to a velocity u given by

1

2ru2 p rV

2H

R;

u

V 2H

R

1=2:

Hence for the standard SSHE, u 1:37 m/s.The significance of this centrifugal effect is that if can cause a series

of fairly stable vortices to be set up between and travel with the blades.

Figure 11 shows this effect. This implies that the outer dimension of the vortex

is equal to the gap width H and that the mixing length L lies somewhere

between H and 2H. Because this is about a tenth of the distance between the

blades, the heat transfer should be increased by a factor of 23.

Figure 11. Vortices behind the blade (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd.,



The vortices need some time to establish, and they will be most persistent if

the ratio of the distance between the blade (pR) to the gap width (H) is closeto an integer. For the standard SSHE the ratio is about 13.

3. Enhancement of annular gap instabilities. The instability of the previous

section will be suppressed by higher viscosities, again reverting to mass rota-

tion. There are different methods used to overcome this with varying degrees

of success:

Oval tubes

Oval shafts

Eccentric shafts

Sectioned shafts

The first three are clear from their description. The sectioned shaft equipped

with staggered blades has large flats to accommodate the blades on opposite

sides, so that the gap widths vary between 9 and 17 mm. Figure 12 shows a

diagram of such a shaft. The effect of the staggered blades is that the position

of the flat is rotated through 90 with each successive blade set. Thisarrangement has other advantages and will be explained later.

The last three design concepts listed have the common feature that the gap

width at a point on the cooling cylinder will vary as the shaft rotates. In the

case of the oval tube the gap width varies when seen from a point rotating

with the shaft.

Figure 12. Sectioned shaft (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd., Reading,

United Kingdom.


Figure 13 illustrates this variation in gap width for the case of the oval shaft

and the sectored shaft. An eccentric shaft would also have a sine-type

function but with only one maximum per revolution.

The key feature of these designs is that the change in gap width creates a

radial velocity equal to dH=dt at the shaft surface. This also has the ability togenerate vortices within the gap.

As Figure 14 illustrates, the advantage of the sectored shaft is that it has

pulses of much greater velocity than the oval shaft followed by periods in

which the turbulence is allowed to develop.

4. Axial flow. The axial velocity of the material through the annular gap is at a

much lower velocity than the rotational velocity. It can, however, still contri-

bute to the creation of instabilities when the staggered blade configuration

is used. This is because, as the material progresses through the cylinder,

it encounters variations in gap width as illustrated in Figure 15. At each

of the changes in cross-sectional areas there is the possibility to induce

turbulence.

Figure 13. Influence of shaft type on gap width (56). Courtesy of N. Hall Taylor, Crown

Chemtech Ltd., Reading, United Kingdom.

Figure 14. Influence of shaft type on rate of change gap width (56). Courtesy of N. Hall Taylor,

Crown Chemtech Ltd., Reading, United Kingdom.


Refrigeration System and Scraped-Surface Units. Scraped-surface heat ex-

changers for margarine production are, as mentioned, designed for direct expansion

refrigerants such as ammonia and Freon 22. Advantage is taken of the high rate of

heat transfer due to surface boiling of the refrigerant (54).

A-units with individual refrigeration systems per cooling cylinder assembly

are available from most suppliers. From Figure 16, an A-unit with four cooling

cylinders with individual refrigeration systems can be seen. Each cooling cylinder

is mounted with a surge drum above the cylinder. The surge drum is part of the

refrigeration system of each cylinder. Figure 17 shows how the refrigeration system

of an A-unit cooling cylinder assembly operates.

During normal operation, all stop valves around the A-unit are open. The liquid

refrigerant inlet solenoid valve (A) is open, allowing liquid to pass through the level

control valve (B) and into the bottom of the refrigerant jacket surrounding the

Figure 15. Change of gap with axial flow (56). Courtesy of N. Hall Taylor, Crown Chemtech Ltd.,


Figure 16. Chemetator SSHE for margarine processing. Courtesy of Crown Chemtech Ltd.,



Figure 17. Schematic diagram of refrigeration system. Courtesy of Crown Chemtech U.S.A., a division of Crown Iron Works Co., Minneapolis, Minnesota.

484

cylinder. Rapid heat transfer through the cooling cylinder wall from the warm

product inside the cylinder causes a considerable proportion of the liquid refrigerant

to vaporize upon contact with the outside wall of the cooling cylinder. Gas and

entrained liquid are discharged from the top of the jacket into the surge drum.

To ensure flooded conditions at all times in the jacket, a liquid level is maintained

in the surge drum by a sensor linked via a capillary tube to the control valve (B).

Gas leaves the surge drum via a pressure regulating valve (C) and the suction

to the suction trap of the fridge plant. The system is controlled by the pilot valve

mounted on the control valve (C). On manual systems, this is adjusted by hand

to give the desired temperature indication on the pressure gauge. On automatic

systems, this is linked via controller to the liquid temperature measuring device

(G) (57).

A current measuring device on the drive motor to the A-unit detects a rise

greater than a predetermined level above the normal running current, typically

10%, for the specific product being processed. This automatically closes the liquid

inlet valve (A) and the pressure regulating valve (C) while keeping the A-units

shaft rotating (54, 57). Normally, a warning signal is given to the operator of a

potential freeze-up, which may be prevented if the problem can be identified and

corrected. The system is then reset manually. If the problem is identified, such as

failure of the high-pressure feed pump, it is possible to prevent a certain freeze-up

by operating a hot-gas system either manually or automatically. This system is lined

electrically, so that it will only operate if valves A and C are closed. Selecting the

hot-gas option opens valves E and D. This immediately allows hot gas from the

high-pressure discharge side of the compressor to be introduced directly into

the refrigerant jacket of the A unit. The pressure in the jacket and surge drum rises

and forces all the liquid out via valve D and the suction line into the suction trap of

the refrigeration plant. Once the liquid is ejected, and assuming that the A-unit shaft

is still rotating, the hot-gas system can be switched off manually or automatically

through an electrical time delay relay. The system will then be ready for restart

when the original problem has been corrected.

In certain parts of the world, power cuts can occur frequently and cause problems

in the operation of A units for margarine production. Due to this, A units are usually

mounted with various features in the refrigerant system to minimize the downtime

related to power cuts. The hot-gas option is one feature. At the moment of the

power cut, valves D and E will automatically open and valves A and C will close.

Although the fridge compressor will also stop running, the residual hot gas in

the condenser and pipework will cause an immediate rise in the pressure in the

refrigerant jacket of the A unit. Although the A-unit shaft has stopped rotating,

this should allow it to rotate freely when power is restored. It is, however, import-

ant that this should nevertheless be checked manually after all necessary safety

precautions have been taken by isolating the drive motor locally or at the electrical

control panel (57).

Following a power cut, product feed failure, or any other abnormal conditions,

it is possible that the A unit will be frozen solid. In this situation, the hot-gas system

can be operated, as described, together with the warm water circulation through the


A-unit shaft to ensure rapid melting of the solidified margarine inside the cooling

cylinder.

Other systems used in A units to help prevent freeze-up situations, as described

above, operate by a drop tank principle, where the refrigerant is removed from

the refrigerant jacket with the aid of increased refrigerant pressure in the system

without installation and activation of a hot-gas system.

2.3. Worker Units

Fats require time to crystallize. This time is provided in crystallizers normally

called worker units, or B units. These are cylinders with larger diameters mounted

with pins on the inside of the cylinder walls (stationary pins) and on the rotors

(rotating pins) (3, 54, 55). The pins fixed to the concentric rotor are mounted in

a helical arrangement that intermesh with the stationary pins of the cylinder wall

(55). Worker units can be installed either between cooling cylinders of a multi-

cylinder. A unit or after the A unit (3, 4, 51, 54, 55, 58). Worker units have the bene-

fit of giving the margarine emulsion time to crystallize under agitation by the pins

of the rotating rotor (see Section 1).

The worker unit is normally mounted with a heating jacket for tempered water

on the cylinder and often also equipped with its own built-in water heater and

circulation pump for the tempered water. This is advantageous in preventing

product buildup on the cylinder wall and allows better product temperature control

during the passage through the worker unit. Product temperature increases of 2C ormore due to release of latent heat of crystallization and mechanical work can be

observed in the worker unit (3).

Worker unit cylinders usually have product volumes ranging from 35 L up

to approximately 105 L per cylinder. B units with up to three worker cylinders

mounted on the same support frame are available on the market. Each worker cylin-

der usually has its own individual drive with fixed or variable speed for maximum

flexibility during processing of margarine. The design of a worker unit is illustrated

in Figure 18.

2.4. Resting Tubes

When producing margarine for stick or block wrapping, a resting tube is normally

connected directly to a packaging machine to allow the product sufficient time to

attain a hardness that is suitable for wrapping (3, 4, 54, 55). During production of

table margarine for stick wrapping, the product will commonly pass through the

cooling cylinders of the A unit and a possible intermediate worker unit (B unit)

inserted between the cooling cylinders. From the A unit, the product enters the

resting tube connected directly to the packaging machine (3).

The intermediate worker unit normally has a lesser product volume than final

worker units used in production of soft table margarine for tub filling. The purpose

of limiting the amount of work given to the product is first to produce a product that

is not too soft to be handled in the automatic stick wrapping machine. Second, it is


to prevent the aqueous phase of the margarine from being dispersed in an extremely

fine state of subdivision (54), which could have a negative effect on the flavor

release. Finally, too intensive working of a table margarine, with its higher solid

fat content compared to a soft margarine, could cause the product to attain an

unpleasant, greasy consistency (59). Too greasy a consistency could also cause

the wrapping material to stick to the product, which would result in a poor presen-

tation of the product to the consumer. Figure 4 illustrates the process flow for

production of table margarine for stick wrapping.

The margarine is forced through the resting tube by the pressure of the high-

pressure feed pump. Resting tubes are normally fitted with screens or perforated

plates (55) to allow a minimal degree of work to be given to the product to ensure

optimal crystallization and plasticity.

Figure 18. Worker unit (B unit) with one cylinder. Courtesy of Crown Chemtech U.S.A., a

division of Crown Iron Works Co., Minneapolis, Minnesota.


Resting tubes for table margarine and similar products are made up of flanged

sections with lengths varying from approximately 450 mm (17.5 in.) to approxi-

mately 900 mm (35 in.) (54, 60). This allows the product volume of the resting

tube to be varied in accordance with the physical characteristics of the solidifying

margarine (54). Resting tubes for table margarine production commonly have dia-

meters ranging from approximately 150 to 180 mm (6 to 7 in.) (54, 60). Resting

tubes for production of puff pastry margarine usually have diameters ranging

from approximately 300 to 400 mm (12 to 16 in.). The flanged section in these

resting tubes has a length of up to approximately 1000 mm (39 in.). The volume

of resting tubes for puff pastry margarine is normally considerably larger than

for other products to allow sufficient time for development of the special consis-

tency required in puff pastry margarine (see Section 5.2).

Some equipment suppliers recommend using one single resting tube for feeding

table margarine to the packaging machine, whereas others recommend the use of

two connecting, parallel resting tubes. When one of the two resting tubes has been

filled with product, a motor-actuated rotary valve automatically switches the flow

of product to the second resting tube. The product in the first resting tube remains

static until the second resting tube has been filled.

The construction of a resting tube usually involves the required inlet adaptor,

flanged sections, screens or perforated plates, and an outlet connection flange for

direct linkup to the packaging machine. Alternatively, the resting tube could also

be mounted with an outlet extrusion nozzle, in case the product is fed to the pack-

aging machine through the older, open hopper system. Resting tubes are normally

jacketed for warm water circulation to minimize the friction between the margarine

and the stainless steel wall of each section. This helps prevent channeling of

the product and reduces the overall discharge pressure required at the high-pressure

feed pump.

Figure 19 shows resting tubes of varied sizes for puff pastry margarine.

2.5. Packaging Equipment

Margarine products are packed in several ways depending on margarine type,

product consistency, and consumer preferences. In the U.S. market, consumer

retail margarines and related products, including butter blends, cover a variety of

products packaged in different ways (61). These can be grouped as follows:

Margarine in quarter-pound sticks

Margarine in one-pound solids

Margarine patties

Soft margarine in tubs

Spreads in quarter-pound sticks or one-pound solids

Soft spreads in tubs

Diet products in sticks or tubs

Liquid margarine in squeeze bottles.


Figure 19. Resting tubes for puff pastry margarine. Courtesy of Crown Chemtech U.S.A., a division of Crown Iron Works Co., Minneapolis, Minnesota.

489

Margarines for food service or industrial use are normally filled into 50-lb plastic

bag lined cartons, wrapped in blocks of 5 lb or bigger, or supplied in bulk.

Stick/Solid Retail Margarine. Two basic types of stick or solid packaging

machinery are used in the United States (62). The first of these forms is a molded

print that forces product into a measuring and molding chamber. The molded print

is removed from the chamber and then wrapped and cartoned. On the second type

of machine, the product from the resting tube is filled directly into a cell that is

prelined with a preformed wrapper bag. The wrapping is then folded and ejected

from the cell.

The second type of machinery is the more widely used type in the U.S.

margarine industry. The principle operation of the second type of machine is shown

in Figure 20. This type of packaging machine was originally developed by Benz &

Hilgers GmbH of Neuss, Germany, and today a wide range of machines for stick or

solid wrapping based on this concept exist (63). The concept shown in Figure 20

involves a machine with drive elements running in an oil bath. The product can be

fed to the machine either by a trough with feed worms or by direct linkup to a rest-

ing tube. Machines of this type can also be fed by a vertical funnel with a special

scraper/agitator mounted. This type of feeding arrangement is normally used when

wrapping miniportions at low hourly capacity.

In Figure 20, the wrapping material is fed continuously from a changeable reel

and is cut crosswise by a knife system before arriving at the bag forming station.

A plunger guides the wrapper through folding channels to form the bags, then

positions the bags exactly into the cells located in the intermittently running rotary

table in the center of the machine (64). The positioned bags are transported by

the rotary table to the dosing station. At the dosing station, the cells are lifted

Figure 20. Forming of the wrapper bag, filling, and folding. Courtesy of Benz & Hilgers GmbH,

Neuss, Germany.


with the wrapper inside to ensure air-free filling of the product. Product is filled into

the preformed wrapper bags by the dosing station utilizing a dosing cylinder with a

piston. After subsequent folding and calibrating station, sharp-edged sticks or solids

are transported out of the packaging machine to the cartoning machine. Figure 21

shows an example of a packaging line including the stick wrapping machine and an

attached cartoning machine.

This packaging operation is more suitable for softer products than the system

where the product is molded before wrapping (62). Furthermore, the described

system normally operates with a bottom fold principle, which facilitates the folding

and closing operation during wrapping of softer product (64). A more economical

length-side fold principle can also be used in the packaging operation, saving

wrapping material. The two folding principles are shown in Figure 22.

The wrapping materials used in the wrapping operation shown in Figure 20

may be parchment, laminated aluminum foil, plastic-coated material, or plastic

foil (63). For packaging of margarines, the first two wrapping materials are com-

monly used.

Generally, packaging lines as shown in Figure 21 used in the margarine industry

are becoming quite sophisticated, involving electric and electronic monitoring

systems to control the functional sequences of the machinery. Monitoring systems

cover registration of production data, identification of end of wrapping material

roll, product pressure control, photoelectric wrapper registration, and automatic

control of dosing volume by integrated check weigher (63). Computer-aided

machine diagnostic systems can also be installed in packaging machinery. This

involves a programmable logic controller (PLC) monitoring system, which helps

to avoid faults in the packaging operation, to identify reasons for failure, and to

control production data.

High-speed, fully automatic packaging lines for stick wrapping of margarine

with speeds up to 240 sticks per minute are widely used in the U.S. margarine

industry. Such lines include fully automatic cartoning machines for inserting four

Figure 21. Example of a packaging line. Courtesy of Benz & Hilgers GmbH, Neuss, Germany.


quarter-pound sticks into one carton, for example. The cartons can then be packed

into cases in semiautomatic case packers or fully automatic wrap-around case

packers. Finally, the packaging lines can also include automatic palletizing

machines. Figure 23 shows a fully automatic, high-speed stick wrapping machine

complete with cartoning machine.

Soft Tub Margarine. In the North American market, soft margarine and spreads

are usually filled into tubs made from either polypropylene (PP) or polyethylene

(PE). Polypropylene allows for a thinner wall of the tubs and is more rigid then

PE. Due to the more rigid structure of PP, tubs made from PP can crack. Tubs

made from PE have a smaller tendency to crack, as PE is more flexible. Due to

this, lids are normally made from PE. Polyethylene gives a better weight control

during the manufacture of tubs, whereas PP in larger quantities is cheaper than

PE. Polypropylene and PE have equal properties in permeability of ultraviolet light

and air (oxidation) (65).

Tub filling machines for margarines and spreads are available from several

U.S. equipment manufacturers such as Rutherford of Rockford, Illinois, Phoenix

Engineering of Wisconsin, and Osgood of Clearwater, Florida.

In tub filling operations, it is normally required for hygienic and easy cleaning

procedures that the filling machine have a clear separation of the mechanical drive

and the product conveyor. Furthermore, it is advantageous to have filling machines

that prevent product or cleaning agents from entering the mechanical drive (66).

Cleaning of tub filling machines is normally limited to those parts in the conveyor

Figure 22. Packets with bottom and length-side fold. Courtesy of Benz & Hilgers GmbH, Neuss,

Germany.


area that are in contact with the product. The dosing module and the entire area in

contact with the product can be automatically CIP (clean-in-place) cleaned in more

sophisticated machines.

Most tub filling machines are in-line machines with up to four tracks depending

on the requirements of filling volume and capacity.

Tub filling machines can be fitted with a variety of functions depending on

whether the margarine is packaged in tubs with a heat-sealed membrane or cover-

leaf under the lid, for example. The main functions of a tub filling machine for

margarine normally are (67):

Tub feeding station with magazine

Direct product feed with pneumatically operated compensating piston

Dosing device with filling nozzles

Feeding of snap-on lids

Press-on station for lids

Date coding device

Off-conveyor

Control panel

Optional functions usually include:

Tub cleaning or sterilization device

Automatic CIP cleaning system

Coverleaf station with magazine

Sealing membrane station with magazine

Other functions

Figure 23. Stick wrapping machine with cartoner. Courtesy of Benz & Hilgers GmbH, Neuss,

Germany.


In margarine production, the packaging line for tubs can be completed with

wraparound case packers and palletizers (67). A fully automatic tub filling machine

is shown in Figure 24. A device for the simultaneous quantitative regulated filling

of liquid or soft plasticized substances, such as butter, margarine, pastes, or the like,

by means of nozzles into adjacently arranged containers with the assistance of at

least one control element interchangeably switchable from filling to discharging

and at least one dosing piston has been described (68).

Industrial Margarines. These products are usually filled into plastic-bag-lined

cartons of various sizes. Special bakery margarines, such as puff pastry margarines,

are normally wrapped in blocks of approximately 125 kg. Alternatively, puff

pastry margarine can be packed in plates or sheets of 15 kg (68, 69). Edmunds

and Budlong (69) have given a detailed description of a continuous sheeting and

packaging machine for puff pastry margarine and related products.

Block and plate wrapping machines for margarines are available today from

C. Bock & Sohn Maschinenfabrik of Norderstedt, Germany, and Gerstenberg &

Agger A/S of Copenhagen, Denmark.

Block packing machines are today quite sophisticated, and it is possible to wrap

different block sizes in one machine. Block packing machines can be delivered with

special slicing equipment for slicing the block during extrusion but before the final

wrapping as illustrated in Figure 25. Block packing machines can, if required, be

installed for automatic CIP cleaning, which is important especially in connection

with butter production (70).

Figure 25 shows a fully automatic block production line where the product to be

wrapped is fed from the SSHE plant into a dosing station. With the help of product

Figure 24. Fully automatic tub filling and closing machine. Courtesy of Benz & Hilgers GmbH,

Neuss, Germany.


Figure 25. Fully automatic block wrapping machine. Courtesy of C. Bock & Sohn Maschinenfabrik, Norderstedt, Germany.

495

and compensator pressure, it is passed on through two laterally placed cylinders via

the resting tube toward the mouthpiece of the block packing machine. Exact weight

control is achieved by the piston stroke of the coupled dosing pistons mounted in

the two cylinders. The extrusion nozzle of the block packing machine is equipped

with a special cutoff device that cuts the product vertically from top to bottom after

finished dosing. The wrapper is fed from the reel, cut, and positioned automatically

under the extrusion nozzle or mouthpiece. The product block arrives onto the wrap-

per, which is supported by a transport plate. Each wrapper will be controlled in its

final position before dosing takes place. A no-wrapper/no-dosing device is mounted

in the machine. Vacuum will hold the wrapper correctly on the transport plate while

the block moves toward the folding level. Here the prefolded block will be trans-

ported by a chain conveyor to the various folding stations. The wrapped and folded

block leaves the machine on a transport belt (69).

Modern sheet wrapping production lines function after the same principles

except that the product is extruded as a sheet or plate from the mouthpiece verti-

cally into a plate turner. Before the extrusion, the wrapper is positioned and follows

the product into the plate turner. The plate turner is driven by a four-step gear drive

rotating the plate turner 90 while the cross-folding takes place between each dos-ing/extrusion cycle. In a horizontal position the plate is pushed out on a conveyor

belt and transported through a permanent folding device for end folding below the

wrapped plate (70).

2.6. Refrigeration Plants

Refrigeration is a key operation in the margarine production plant. In the margarine

industry, Freon 22 and ammonia were widely used as refrigerants. New regulations

phasing out the use of chlorofluorocarbons (CFCs) are in place in many countries

for environmental reasons (see Section 3). Plans for phasing out a hydrochloro-

fluorocarbon (HCFC) such as Freon 22 (R-22) are currently being made or in

some countries are already in place (52, 71). The layout of an ammonia compressor

plant servicing an SSHE for margarine production can be seen in Figure 17 (see

Section 2.2).

Ammonia systems consist of a compressor designed to compress the low-

pressure ammonia gas from the SSHE. The gas is then discharged from the

compressor into the condenser. When ammonia is under a pressure of 150 psi

(10 bar), it will liquify at a temperature of 25.6C (78F) (71). Condensers canbe of the air-cooled or water-cooled type covering also evaporative condensers

(72). From the condenser, the liquid ammonia flows to the receiver. The receiver

in which the high-pressure ammonia liquid is stored maintains a constant supply

of refrigerant to the SSHE.

Figure 26 shows a packaged ammonia compressor system designed for servicing

an SSHE in margarine production. The system is skid-mounted from the factory for

easy installation. Only the condenser of the system is supplied loose.

Ammonia compressor systems used in margarine plants are usually equipped

with highly efficient superseparators for removal of lubrication oil from the


ammonia (71). Lubrication oil carried over into the ammonia will eventually reduce

the heat transfer efficiency of the SSHE, as the oil will be deposited as a thin film on

the outside wall of the cooling cylinder. This can reduce the heat transfer consider-

ably. Compressors of the reciprocating piston type or screw compressors are nor-

mally installed depending on compressor cost at various capacities or individual

preferences (71). The screw compressors, with their highly efficient coalescing

separators, reduce the amount of oil in the system considerably (70).

The use of ammonia as a refrigerant in margarine plants offers certain advan-

tages as well as disadvantages. The advantages are cost, efficiency, detection, and

environment (70). The quantity of refrigerant needed to charge an ammonia system

is substantially less than for other systems, which provides additional savings.

Ammonia is the most efficient of the commonly used refrigerants. Easy detect-

ability of ammonia leaks is an advantage compared to R-22, taking into consi-

deration the latest enforcement laws by the U.S. Environmental Protection

Agency (EPA). Finally, ammonia is biodegradable and has no impact on the ozone

layer (71).

The disadvantage are toxicity and flammability. Ammonia has a corrosive effect

on tissues and can cause laryngeal, bronchial spasm and edema, which lead to

obstructed breathing. Ammonias flammability range in air is 1625% by volume.

It is usually characterized as hard to ignite (71). A suitable ammonia detection

system with alarm should be installed and well maintained. Detectors should sound

an alarm at the lowest practical level, not to exceed 1000 ppm.

Due to the disadvantages of ammonia, a number of regulations and standards

provide safe practice procedures for the use of ammonia as a refrigerant. Details on

mechanical requirements of refrigeration systems can be found in ANSI/ASHRAE

Standard 15, Safety Code for Mechanical Refrigeration. Piping requirements

should comply with ANSI B31.5, Refrigeration Piping (70). Many local and

national codes must also be complied with in many states.

Figure 26. Packaged ammonia compressor system. Courtesy of Cremeria Americana SA,

Mexico.


3. REFRIGERANTS FOR THE FUTURE

A number of new refrigerants have been proposed during the last several years as

candidates to replace R-22 and R-502 in industrial refrigeration systems (73). Inter-

national accords such as the Montreal Protocol on CFC production and other

accords concerning pollution and gas emissions to the atmosphere in particular

prompt a review of the refrigerants used in the margarine industry (52, 74).

Studies of the CFC refrigerants ozone depletion and its effect on the ozone layer

and global warming have reached such serious conclusions that both national and

international accords are in place to protect the environment (52, 71, 74).

R-22 is an HCFC refrigerant considered to have an ozone depleting effect only

5% of that of a CFC refrigerant such as R-12 (52). Replacements for R-502 are

being announced earlier than replacements for R-22 by refrigerant manufacturers.

This is due to the early deadlines for ending production of ozone-depleting CFC

refrigerants such as R-115, which is a component of R-502 (73). New refrigerants

to replace R-502 and R-22 are discussed in detail in the literature (73, 74).

Well-known biodegradable but toxic ammonia currently is emerging as the leading

replacement refrigerant (71).

The industry should already consider the effects of the new environmental

policies on its possible need for new refrigeration equipment or for modification

of existing equipment (71, 74).

New alternative refrigerants may exhibit different heat transfer characteristics

and may quite importantly require different discharge pressures than R-22 under

similar temperature conditions (73). This should be considered very carefully,

and all safety procedure and regulations as well as pressure vessel codes should

be followed closely when modifying existing refrigeration plants (72). Consider-

able information on R-22 and R-502 replacement refrigerants has been developed

by the Alternative Refrigerants Evaluation Program (AREP). AREPs purpose is to

identify the most promising non-ozone-depleting refrigerants (73).

Fluorocarbon products that do not contain chlorine and/or bromine (i.e., fully

fluorinated and hydrofluorinated [HFC] products) are not stratospheric ozone-

depleters, and production of these products is not being eliminated by the Montreal

Protocol. They are, however, restricted by the U.S. Clean Air Act and must be

recovered rather than released to the atmosphere.

As a result of the Montreal Protocol and Kyoto Protocol and subsequent

amendments and ratification by individual countries, there are current and propos-

ed regulations limiting the production, consumption, and trade of CFCs, HCFCs,

and HFCs. Over the past two decades, the global fluorocarbons market has

undergone a number of major transitions toward a greater use of non-ozone-

depleting HFCs and non-global-warming, nonfluorocarbon alternatives in emissive

or potentially emissive applications.

Compared with the United States, the European Union has been significantly

more aggressive in its production reduction to date and scheduled reduction of

HCFC production, and it is considering restrictions in the use of HFCs in compli-

ance with Kyoto Protocol goals to limit the emissions of global warming gases.


HFCs, FCs, and other fluoro-based compounds are some of the alternatives to

HCFCs and CFCs (75).

4. PLANT LAYOUT AND PROCESS FLOWSHEET

In margarine production, raw materials account for about 50% of the margarine

cost, actual production costs account for 20%, and other costs are 30% of the total

(35). Well-managed formulation and efficient, accurate metering/weighing systems

for the various raw materials in the emulsion preparation plant are essential factors

for cost-efficient margarine production (35, 7678).

Table 2 can be used to illustrate the significance of the cost of the various ingre-

dients in a specific recipe for production of 1 ton of margarine.

Microcomputers, allow the optimizing of formulation cost or least-cost formula-

tion. One method is to select from the formula file according to fluctuations in raw

materials prices. The high number of formulas required can make this task quite

difficult unless computers are used to sort out the least-cost formula. Production

schedules and previous purchases of raw materials will also have to be considered

(35).

Another method is to create new formulations by minimization. Here formula

cost is optimized against constraints. These constraints are based on finished pro-

duct characteristics in relation to raw material characteristics. Production cons-

traints relate to raw material properties, existing and new processes as well as

productivity in the plant. It is essential to compare formulas and processes in order

to optimize productivity by minimizing metering or weighing errors during emulsion

TABLE 2. Ingredient Cost (79).

U.S.

Ingredient % in Recipe $/Ton Margarine

Soybean oil, hydr. 44/46C 32.00 190.30(111.2/114.8F)

Soybean oil, hydr. 34/36C 4.00 23.79(93.2/96.8F)

Soybean oil 44.00 213.22

Emulsifier 0.20 5.98

Lecithin 0.20 1.61

Color (carotene) 0.005 12.65

Aroma 0.02 8.05

Water 16.935 0.14

Salt 2.00 3.91

Milkpowder 0.50 23.00

Potassium sorbate 0.10 8.40

Citric acid 0.04 2.53

100.0 493.58

From Crown Wurster & Sanger, Minneapolis, Minnesota, with permission.

PLANT LAYOUT AND PROCESS FLOWSHEET 499

preparation and the use of unsuitable formulas. This will help to minimize the

amount of product that has to be recycled. In a high-productivity setting, reworked

or recycled product should constitute no more than 0.10.2% of the total plant

production. Product specifications, fulfillment of these specifications, and product

consistency as well as expected technical performances of the product are quality

constraints. Depending on the quality control efficiency, recycling losses may reach

0.20.4% of the total production. Raw material quality is usually the cause (35).

Emulsion preparation systems play a very important role for achieving the above

productivity and thus the desired profitability in margarine production. Three gen-

eral systems are normally used for metering and mixing the various ingredients into

a water-in-oil emulsion. These are (80):

A continuous metering pump system

A batchwise scale tank system

A batchwise flowmeter system

4.1. Continuous Metering Pump System

The margarine industry, like other food processing industries, is continuously

involved in optimizing productivity through rationalization to minimize production

costs. To achieve this a proper production method and production installation must

be chosen allowing optimal capacity at minimal labor cost, maintenance cost,

space, and energy requirements. At the same time the high product quality and

productivity must be assured (81).

Continuous emulsion preparation using a metering pump system has been suc-

cessfully used during the last decades in the margarine industry to meet the above

requirements (76, 78) and is considered to be a very flexible installation (53).

Well-known suppliers of metering pump systems are Bran Luebbe Inc. of BuffaloGrove, Illinois, and American Lewa Inc. of Holliston, Massachusetts.

In connection with the use of continuous metering pump systems, metering

or dosing can be defined as the addition of a defined ingredient flow or amount

(ingredient flow is equal to the ingredient amount added over a specified time

period) to a process tank, a mixer, or a process (81).

To allow metering, the ingredient flow (i.e., ingredient amount) must be trans-

ported, metered, and added. The metering pump covers the three operations of

transport, metering, and addition in one step. Thus, the metering pump differs

from regular pumping applications by two characteristics (81):

1. The flow is easily adjustable in a defined way.

2. Pressure and viscosity variations have no or only minimal influence on the

flow.

A metering pump consists of drive with gear reducer and a pumphead, where the

gear reduces the rotary motion of the drive motor and coverts it into a reciprocating


plunger motion. Suction and discharge valves work alternately according to the

plunger stroke. The capacity is determined by plunger diameter, stroke length,

and stroking speed and can be adjusted manually, electrically, or pneumatically

(8183).

A combined adjustment of stroke length and stroking speed will allow the

proportional metering of two or more ingredient flows based on the use of

multiple pumpheads (79). Due to the flexibility of the metering pump, margarine

emulsion preparation can be fully or partly automated by the use of a metering

pump system with multiple pumpheads. For example, only two pumpheads are

used for metering of the oil phase and the water phase.

Plunger diameter, stroke length, and type of stroking speed adjustment can be

chosen individually for each pumphead in the multiple pumphead metering pump

system (8183).

In margarine production it is possible to install a multipumphead system with

indiv

Margarine 12

Documents

Transcript of Margarine 12