Gas i Fiction

8/2/2019 Gas i Fiction

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COMBUSTION GASIFICATION PROPULSION

LABORATORYDEPT OF AEROSPACE ENGINEERING

INDIAN INSTITUTE OF SCIENCES

BANGALORE INDIA

Gasification (Heat & Power)

Technology of Gasification

1. Concept and Principle

Gasification is the process of converting solid fuels to gaseous fuel. It is not simply pyrolysis;pyrolysis is only one of the steps in the conversion process. The other steps are combustionwith air and reduction of the product of combustion, (water vapour and carbon dioxide) intocombustible gases, (carbon monoxide, hydrogen, methane, some higher hydrocarbons) andinerts, (carbon dioxide and nitrogen). The process leads to a gas with some find dust andcondensable compounds termed tar, both of which must be restricted to less than about 100ppm each if the gas is to be used in internal combustion engines.

2. Uses of Producer Gas

The producer gas obtained by the process of gasification can have end use for thermalapplication or for mechanical/electrical power generation. Like any other gaseous fuel,producer gas has the control for power when compared to that of solid fuel2.1 Thermal

Thermal energy of the order of 5 MJ is released, by flaring 1 m3 of producer gas in theburner.

2.2 Power Generation

Using wood gas, it possible to operate a diesel engine on dual fuel mode. Diesel substitutionof the order of 80 to 85% can be obtained at nominal loads. The mechanical energy thus

derived can be used either for energising a water pump set for irrigational purpose or forcoupling with an alternator for electrical power generation, either for local consumption


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3. Wood Gasifier

This system is meant for biomass having density in excess of 250 kg/m3. Theoretically, theratio of air-to-fuel required for the complete combustion of the wood, defined as

stoichiometric combustion is 6:1 to 6.5:1, with the end products being CO2 and H2O.Whereas, in gasification the combustion is carried at sub-stoichiometric conditions with air-to-fuel ratio being 1.5:1 to 1.8:1. The product gas thus generated during the gasification processis combustible. This process is made possible in a device called gasified, in a limited supplyof air. A gasifier system (Fig. 1) basically comprises of a reactor where the gas is generated,and is followed by a cooling and cleaning train which cools and cleans the gas. The cleancombustible gas is available for power generation in diesel-gen-set. Whereas, for thermaluse the gas from the reactor can be directly fed to the combustor using an ejector.

4. Gasifier Specification


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WOOD TO ENERGY CONVERSION DATA

BEFORE GASIFICATION

Based on wood moisture content of 15% wet basisWoods gross heat energy content: 15,490 kJ per kgWoods gross heat energy content: 6,600 BTU per lb

Or 4.3kW heat per kg. Or 2.615HP per lb

Gasifiers energy conversion efficiency: 73.57% HOT GAS

Gasifiers energy conversion efficiency: 70.95% COLD GAS

AFTER GASIFICATION

Gas produced from 1kg of wood: 2.185 standard cubic metresGas produced from 1lb of wood: 35 standard cubic feet

Energy content of 1 standard cubic metre of gas: 5,030kJEnergy content of 1 standard cubic foot of gas: 135 BTU

After gasification 1kg wood yields 2.185 cubic metres of gas which has a nett heat energy

content of 3.05kW heat.

After gasification 1lb wood yields 35 cubic feet of gas which has a nett heat energy contentof 1.8566HP heat. (Or 4,725 BTU)

1kg of wood produces 2.185 cubic metres of gasor 3.165kW heat from burning gas direct

or 0.837kW of shaft power i.e engineor 0.754kW of electric power generated

1lb of wood produces 35 cubic feet of gas

or 4,900 BTU heat from burning the gas director 1.925HP heat from burning the gas direct

or 0.51 HP of shaft power i.e engine

or 0.459HP of electric power generated

or 0.342kW of electric power generated

1 litre of diesel has a heat energy content of 9.630 kW heat (or 32,895 BTU)1 litre of petrol as a heat energy content of 8.79 kW heat (or 30,023 BTU)

1 litre of diesel has the same heat energy content as the cold gas from 3.1579kg of wood1 litre of petrol has the same heat energy content as the cold gas from 2.882kg of wood


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INDICATIVE, WOOD WEIGHTS AND GAS VOLUMES REQUIRED

AND

INDICATIVE, SHAFT AND ELECTRIC POWER OUTPUTS

FOR ENGINES AND GENERATOR SETS

Fuelled with PRODUCER GAS from biomass (wood)

(tabulated values are per 100 cubic inches of total cylinder displacement (4 cycle))

Engine RPM 1200 1400 1500 1600 1800 2000 2200 2300

Spark IgnitionEngines

Wood requiredin lbs/hr

18.426 21.457 22.989 24.521 27.588 30.652 33.715 35.251

Gas requiredin cu'ft'/hr

648.1 752.26 810.127 864.06 972.1531080.07

1188.11

1242.1

Shaft horsepower

9.375 10.937 11.717 12.5 14.065 15.625 17.187 17.968

Electric powerin kW.e

6.116 7.135 7.646 8.156 9.177 10.193 11.214 11.724

Dual fuel,diesel enginesfuelled withdiesel plusproducer gasNOTE: Woodand gasrequired is thesame as forspark ignitionengines

Shaft horse

power

11.718 13.671 14.647 15.625 17.581 19.53 21.484 22.46

Electric powerin kW.e

7.645 8.92 9.557 10.195 11.471 12.743 14.018 14.654


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To obtain wood and gas required plus power output values for a particular engine:

1. Select the required RPM column

2. Extract the required tabulated 'per 100 cubic inches' value

3. Multiply that value by the particular engines swept volume in whole 100s anddecimals of 100 cubic inches. For example: 350 cubic inches = 3.5

Air Dry Wood Fuel Gross Heat Energy Content = 4.3kW per kg of wood

Wood > Gas > Energy Heat Yield (Hot Gas) = 3.165kW per kg of woodWood > Gas > Energy Heat Yield (Cold Gas) = 3.05kW per kg of wood

Wood to Gas Volume Yield = 2.185m gas per kg wood

Gas > Energy Heat Yield (Hot Gas) = 1.45kW per cubic metre hot gas

Gas > Energy Heat Yield (Cold Gas) = 1.4kW per cubic metre cold gas

Wood > Gas > Shaft Power Spark Ignition Engine (Petrol) = 0.837kW shaft per kg of woodWood > Gas > Shaft Power Spark Ignition Engine (Gas) = 0.82kW shaft per kg of wood

Wood > Gas > Shaft Power Dual Fuel Diesel Engine = 0.86kW shaft per kg of wood

Wood > Gas > Electricity Spark Ignition Petrol EngineGenerator = 0.754kW/hr electricity per kg wood

Wood > Gas > Electricity Spark Ignition Gas Engine

Generator = 0.697kW/hr electricity per kg woodWood > Gas > Electricity Dual Fuel Diesel Engine

Generator = 0.731kW/hr electricity per kg wood

Wood > Gas > Process Heat (Direct) = 3.17kW heat per kg wood

Wood > Gas > Process Steam = 4.465kW steam per kg wood

Wood > Gas > Power Steam = 3.93kW steam per kg wood

Petrol engines run on Producer Gas at recommended, maximum continuous RPM.


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High compression engines derate 37.3% approx to recover power including capacity x 1.6

times

Average high compression engines derate 42.5% approx to recover power includingcapacity x 1.74 times

Medium high compression engines derate 47.0% approx to recover power including

capacity x 1.9 timesLow compression engines derate 56.3% approx to recover power including capacity x 2.3

times

Diesel (Dual Fuel) engines on pilot diesel plus Producer Gas at recommended, maximumcontinuous RPM derate 20% approximately. To recover power including capacity x 1.25

times

Gas engines run on Producer Gas at recommended, maximum continuous RPM

companion ratio: 10 to 1 - derate 10% approximately. To recover power including capacityx 1.1 times


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In a presentation to the U.S. Dept. of Energy-sponsored DEER 2009 conference here,

Cummins Vice President John Wall said his company is enjoying a successful partnership

with Indian Institute of Science (IISc) to develop more gasification-based power projects inrural India.

So far, the scheme in India taps local biomass feedstocks, including coconut shells

and rice husks, at 20% of the cost of conventional diesel fuel, for generator-set power, Wall

said.

But sustainable biomass-gasification power looks to have a promising future inmore areas and more countries beyond just India, Wall pointed out to Gasification News in

a post-conference interview.

We now have more than 10 megaWatts [MW] of power with biomass gasification

in India, Wall told us. Were working on smaller-scale gasification for rural electricity,

and were working with non-governmental organizations to help overcome powershortages in such areas, he said.

Such efforts to improve power availability in relatively impoverished areas not onlyrepresents socially conscious good citizenship, but also can mean development of a

sustainable green business, he added.

Cummins not only provides a modified diesel engine (capable of burning a mix of

synthesis gases) but also the required power electronics and gen-set equipment, he said.

In a separate interview, Cummins-India engineer Anant Talaulicar told us that the

scheme (developed together with IISc-licensed gasification technology) employs multiplesizes of diesel engines that have been modified appropriately to handle biomass based

gases.

The biomass being used is typically wood chips, but also rice husk and coconutshells. We have installed many applications in India successfully now in rural

environments mainly for commercial operations.

R.S. Raman, Senior General Manager for Cummins-India Energy Solutions

Business & Power Electronics, separately added that we have gen-sets in individual poweroutput capacities of 25-KW [kiloWatt], 70-KW, 120-KW and 240-KW. We have executed

some projects up to 1-MW power output using multiple product configurations.

The IISc-licensed gasification scheme (see: link to source document) can tap wood,woody biomass and agricultural wastes including coconut shells.
http://cgpl.iisc.ernet.in/site/Portals/0/Technologies/Gasification%20Technology.pdfhttp://cgpl.iisc.ernet.in/site/Portals/0/Technologies/Gasification%20Technology.pdf


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IISc Biomass Gasifier

Source: Indian Institute of Science

Removal of dry particles/dust is achieved with cyclone filters, while tar and fineparticle emissions are removed by water scrubbers.

The cleaned syngas is then fed through blowers at the engine inlet through a

specially developed carburetor.

Engine exhaust heat is recycled for drying feedstock and as input to chillers.

While the produced gas varies widely depending upon feedstock, chemicalcomposition is generally about 20% carbon monoxide, 20% hydrogen, 3% methane, 12%

carbon dioxide and the balance inert nitrogen, according to Cummins.

Calorific value of the syngas is typically 1,100 to 1,200 Kcal per cubic meter.

For gen-set applications, tar and particulate matter in syngas must be less than 25-

ppm, according to the company.

IISc points out that its cooperative work with Cummins India involves more than

40 gasifier installations, with Cummins providing generator-sets backed with warranties.

With the IIScs gasification technology offering multi-fuel option, there is

flexibility for the end user/client to source biomass based on availability thereby keepingthe cost of power generation at a minimal, according to IISc.

The diverse range of biomass that is being used includes weeds such as ipomea,

prosopis julifora, forest residue to industrial wastes such as sawdust and bamboo dust in


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briquetted/compacted form. Many of these plants are operated round the clock, and the

availability of the plant has been as high as 85% to 90%.

The plant with such high plant load factor is able to provide accelerated return tothe investor apart from additional revenue in the form of by-product such as activated

carbon. Cost of power generation as low as Rs 2.50 per unit electricity generated has beenachieved.

To sum up the performance, currently the technology is making a modest saving toa tune of 20- 25 kilo-liters of fossil fuel per day and saving valuable foreign exchange to

the country. Jack Peckham
mailto:[email protected]:[email protected]:[email protected]


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Calorific value

The calorific value of a fuel is the quantity of heat produced by its combustion - atconstant pressure and under "normal" conditions (i.e. to 0oCand under a

pressure of1,013 mbar).

The combustion process generates water vapor and certain techniques may beused to recover the quantity of heat contained in this water vapor by condensingit.

The Higher Calorific Value (or Gross Calorific Value - GCV) suppose that thewater of combustion is entirely condensed and that the heat contained in thewater vapor is recovered.

The Lower Calorific Value (or Net Calorific Value - NCV) suppose that the

products of combustion contains the water vapor and that the heat in the watervapor is not recovered.

Fuel

Higher Calorific Value(Gross Calorific Value - GCV)

kJ/kg Btu/lb

Acetone 29,000

Alcohol, 96% 30,000

Anthracite 32,500 - 34,000 14,000 - 14,500

Bituminous coal 17,000 - 23,250 7,300 - 10,000

Butane 49,510 20,900

Carbon 34,080

Charcoal 29,600 12,800

Coal 15,000 - 27,000 8,000 - 14,000


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Fuel


kJ/kg Btu/lb

Coke 28,000 - 31,000 12,000 - 13,500

Diesel 44,800 19,300

Ethanol 29,700 12,800

Ether 43,000

Gasoline 47,300 20,400

Glycerin 19,000

Hydrogen 141,790 61,000

Lignite 16,300 7,000

Methane 55,530

Oils, vegetable 39,000 - 48,000

Peat 13,800 - 20,500 5,500 - 8,800

Petrol 48,000

Petroleum 43,000

Propane 50,350

Semi anthracite 26,700 - 32,500 11,500 - 14,000


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Fuel


kJ/kg Btu/lb

Sulfur 9,200

Tar 36,000

Turpentine 44,000

Wood (dry) 14,400 - 17,400 6,200 - 7,500

kJ/m3 Btu/ft3

Acetylene 56,000

Butane C4H10 133,000 3200

Hydrogen 13,000

Natural gas 43,000 950 - 1150

Methane CH4 39,820

Propane C3H8 101,000 2550

Town gas 18,000

kJ/l Btu/Imp gal

Gas oil 38,000 164,000

Heavy fuel oil 41,200 177,000


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Fuel


kJ/kg Btu/lb

Kerosene 35,000 154,000

1 kJ/kg = 1 J/g = 0.4299 Btu/ lbm = 0.23884 kcal/kg 1 Btu/lbm = 2.326 kJ/kg = 0.55 kcal/kg 1 kcal/kg = 4.1868 kJ/kg = 1.8 Btu/lbm 1 dm3 (Liter) = 10-3 m3 = 0.03532 ft3 = 1.308x10-3 yd3 = 0.220 Impgal (UK) = 0.2642 Gallons (US)


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CALORIFIC VALUE OF FUELS

Sr Fuel Approx heating value Kcal/Kg

NaturalState

Drystate

A BIOMASS

1 Wood 1500 3500

2 Cattle dung 1000 3700

3 Bagasse 2200 4400

4 Wheat and rice straw 2400 2500

5 Cane trash, rice husk, leaves and vegetablewastes

3000 3000

6 Coconut husks, dry grass and crop residues 3500 3500

7 Groundnut shells 4000 4000

8 Coffee and oil palm husks 4200 4200

9 Cotton husks 4400 4400

10

Peat 6500 6500

B FOSSIL FUELS

1 Coal 4000-7000

2 Coke 6500

3 Charcoal 7000

4 Carbon 8000

5 Fuel oil 9800

6 Kerosene and diesel 100007 Petrol 10800

8 Paraffin 10500

9 Natural gas 8600

10

Coal gas 4000

11

Electrical (Kcal(KW) 860

12

Bio gas(Kcal/cu mtr) (12 kg of dungproduces 1 cu. Mtr gas)

4700-6000


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2.Calorific value of fuels

Heat energy is measured in units of joules or calories (1calorie = 4.18 joules). The heat generated fuels when they burn in joules or calories measures quality of fuels. All fuels do not burn efficiently. Ththere are fuels that produce more heat than the others are. This can be distinguished in terms of numbof joules or calories that they generate on burning.

The amount of energy generated when 1 unit mass of fuel is burnt completely is known as the calorificvalue of the fuel. The word calorific is used, not joulific because of the use of the word calorific has beein use for a very long time. When 1 gram of charcoal is burnt, it produces 33 kilo joules. Thus the calorifivalue of charcoal is 33kJ/g. Sometimes instead of calorific value, another term kilowatt per kilogram

(KWh/kg) is used. The table below gives the calorific values of some of the common fuels used fordomestic and industrial use.

Type of fuel Fuel Calorific value

kJ/g kwh/kg

Solid Charcoal 33 10.7

. Coal 25.33 8.1

. Wood 17 5.5

. Dung cake 6 to 8 2 to 2.6

Liquid Kerosene 48 15.5

. Petrol 50 .

. Diesel 45 15.5

. Ethanol 30 9.7

Gaseous Bio gas 35 to 40 11.3 to20.9

. Butane (LPG) 50 .

. Methane 55 17.8

. Hydrogen 150 48.5

Later on in the chapter we will see how calorific value is measured. But from the table it is easy tounderstand that comparison between fuels can be done when their properties as fuels is standardized interms of calorific values.
http://home.att.net/physics/heat-I.htm#unitshttp://home.att.net/physics/heat-I.htm#units


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Hydrogen as fuel : Hydrogen gas has the highest calorific value in the table given above. Thus hydrogenis the best fuel but since its transport and handling is difficult, hydrogen is used as fuel where it is

absolutely necessary. Otherwise hydrogen gas as a source of common fuel is not used in domestic or inindustrial situations. Hydrogen gas jet along with oxygen gas is used for producing a very hot flame, whiis used for cutting metals in industries.

Methane or butane as fuel : Both methane and butane produce good amounts of heat. They are ideal fouse as domestic fuels. Since methane has higher percentage of hydrogen than butane, its calorific valueis more. Methane (CH4) has 25% hydrogen and butane (C4H10) has 17% hydrogen.

Wood as fuel : Wood has been traditionally used as fuel. The main content of wood is cellulose(C6H10O5)n. The presence of oxygen in a fuel, helps oxidation but does not contribute to heat or its calorifvalue. In fact it is seen that if a substance contains oxygen, it will produce less heat energy per unit weig

when the substance burns. In wood therefore, the percentage of carbon and wood is quite less. This givwood quite a less calorific value.

How to measure calorific value of a fuel :The method by which calorific value of substances is measured is called a calorimeter. The fuel whosecalorific value is to be measured, is first weighed. Let its mass be g grams. Let m grams of water beheated by this fuel. Measure the temperature of the water before and after the fuel is burnt completely. Lt be the rise in temperature of m grams of water when g grams of fuel is burnt completely.

Heat produced = Q = m x s x t

m = mass of water in grams

s = specific heat of water = 4.2.J/gm x C

t = rise in temperature of the water.

Thus Q amount of heat is generated by g amount of fuel. The calorific value is given by the followingequation.

Calorific value = Q / g joules per gram. (for value in kilo joules, divide by 1000)

The figure above shows an arrangement where a candles calorific value is being measured. Heat thewater for a while and note the rise in temperature.

Let W1 = initial weight of the candle

W2 = final weight of the candle
http://home.att.net/physics/heat-I.htm#Specific%20heathttp://home.att.net/physics/heat-I.htm#Specific%20heat


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W1 - W2 = weight of wax burnt to heat the water.

T1 = initial temperature of water

T2 = final temperature of the water

T2 - T1 = rise in temperature of water.

m = mass of water

s = specific heat of water in J/gm/ C

heat produced m x s x (T2 - T1)

Calorific value of wax = = = J/gmmass of wax burnt (W1 - W2)

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