Hazard and Environmental of Solid wast treatment plant
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Transcript of Hazard and Environmental of Solid wast treatment plant
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Chapter 8 Hazard and environmental considerations
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Chapter 8: Hazard and Environmental Considerations
8.1 Safety and Health Considerations
There is some dangerous in conjunction with our plant operations. These
dangerous areas were divided into toxic hazards, and fire and skin burn hazards.
8.1.1 Toxic Hazards
Carbon MonoxideThe principle fuel component of syngas is carbon monoxide (CO), a deadly
poison that ties up hemoglobin in the blood and prevents the transport of oxygen to
the tissues. Death from CO is death by suffocation. Lesser exposures cause
headaches, nausea, dizziness and irritability. CO is an insidious poison because it is
odorless and tasteless.
Exposure during pregnancy, even at levels too low to show symptoms in the
mother, may affect development of fetus, lower its birth weight and increase the
risk of abortion and stillbirth. There are no indications that CO causes mutations or
cancer.
Seventeen people were killed in Sweden between December 1939 and
March 1941 because of careless gasifier operations. More recently, two researchers
at Midwestern University died from CO inhalation when they climbed inside of a
gasifier fuel bin.
Signs and symptoms of carbon monoxide poisoning may include:
Dull headache Weakness
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Dizziness Nausea Vomiting Shortness of breath Confusion Blurred vision Loss of consciousness
For the first aid treatment of CO poisoning we should do the following steps:
Move the poisoned person to the open air or a room free of CO. If the person is unconscious, administer artificial respiration immediately. Administrate oxygen or mixed resuscitation gas (7%CO2 in oxygen) as soon
as possible.
Keep the victim warm.
Sulfur DioxideSulfur dioxide (SO2) is a moderate to strong irritant. Most inhaled SO2 only
penetrates as far as the nose and throat with minimal amounts reaching the lungs
unless the person is breathing heavily, breathing only through the mouth or the
concentration of SO2 is high.
Sensitivity varies among people, however, short exposure (1-6 hours) to
concentrations as low as 1 ppm may produce a reversible decrease in lung
function. A 10 to 30 minute exposure to concentrations as low as 5 ppm has
produced constriction of the bronchiole tubes. Only one of eleven volunteers
showed any effects at 1 ppm. A 20-minute exposure to 8 ppm has produced
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reddening of the throat and mild nose and throat irritation. About 20 ppm is
objectionably irritating, although people have been reported to work in
concentrations exceeding 20 ppm. 500 ppm is so objectionable that a person cannot
inhale a single deep breath.
In severe cases where very high concentrations of SO2 have been produced
in closed spaces, SO2 has caused severe airways obstruction, hypoxemia
(insufficient oxygenation of the blood), pulmonary edema (a life threatening
accumulation of fluid in the lungs), and death in minutes. The effects of pulmonary
edema include coughing and shortness of breath which can be delayed until hours
or days after the exposure. These symptoms are aggravated by physical exertion.
As a result of severe exposures, permanent lung injury may occur.
If SO2 comes into contact with the skin the gas will react with moisture on
the skin and cause irritation. Liquid SO2 may cause burns due to freezing.
Also SO2 can hurt the eyes, Volunteers exposed to 5.4 ppm SO2 experienced
mild irritation, while 9.1 ppm cause moderate to severe irritation. At 8-12 ppm,
smarting of the eyes and lachrymation (tears) began. There is strong irritation at 50
ppm. In severe cases, (very high concentrations in confined spaces), SO2 has
caused temporary corneal burns. Liquid SO2 can burn the eye and permanently
affect vision. Injury from contact with liquid SO2 may not be immediately noticed
by the victim because SO2 damages the nerves of the eye. Any eye contact should
be treated as very serious.
Several epidemiological studies have examined the possibility that sulfur
dioxide may cause cancers such as lung cancer, stomach cancer or brain tumors.
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Signs and symptoms of carbon monoxide poisoning may include:
Eye irritation. Nose irritation. Throat irritation. Runny nose. Choking. Cough. Frostbite. Skin burns. Chest pain. Breathing difficulty. Tearing eyes. Cyanosis.
For the first aid treatment of SO2 poisoning we should do the following steps:
Breathing exposure Move the poisoned person to the open air or a room free of CO. If the person is unconscious, administer artificial respiration
immediately.
Administrate oxygen or mixed resuscitation gas (7%CO2 in oxygen)as soon as possible.
Transport victim to an emergency care facility.
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Skin exposureGas:
If irritation occurs, flush contaminated area with lukewarm, gentlyrunning water for at least 5 minutes.
If irritation persists, obtain medical attention immediately.Liquid:
Avoid direct contact. Quickly remove victim from source of contamination and briefly flush
with lukewarm, gently flowing water until the chemical is removed.
DO NOT attempt to rewarm the affected area on site. DO NOT rub area or apply dry heat. Gently remove clothing or jewelry that may restrict circulation. Carefully cut around clothing that sticks to the skin and remove the
rest of the garment.
Loosely cover the affected area with a sterile dressing. DO NOT allow victim to drink alcohol or smoke. Quickly transport victim to an emergency care facility.
Eyes exposure Remove source of contamination or move victim to fresh air. Immediately flush the contaminated eye(s) with lukewarm, gently
flowing water for at least 5 minutes for the gas (20 minutes for the
liquid) or until the chemical is removed, while holding the eyelid(s)
open.
Take care not to rinse contaminated water into the unaffected eye oronto the face.
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Obtain medical attention immediately.Provide general supportive measures (comfort, warmth, rest). Consult a
doctor and/or the nearest Poison Control Centre for all exposures except under
minor instances of inhalation or skin contact. Some recommendations in the above
sections may be considered medical acts in some jurisdictions. These
recommendations should be reviewed with a doctor and appropriate delegation of
authority obtained, as required. All first aid procedures should be periodically
reviewed by a doctor familiar with the material and its conditions of use in the
workplace.
From safety standpoint the best gasifier systems operate at negative pressure,
so that leaks result in air being drawn into the system (possibly causing gas
explosions which the equipment is designed to handle without harm) rather than
CO being expelled into the process utility. The importance of achieving a leak-
tight system cannot be overemphasized.
CreosoteIt is the tar, soot and other oils that produced as unwanted products
from the gasification process. It should be scrubbed from the gas and
disposed of.
Health problems caused by creosote exposure
Longer exposure to creosote vapors can irritate the lungs. Exposure to small amounts of creosote over time by direct skin
contact or by contact with creosote vapors, may cause:
Blistering, peeling, or reddening of the skin. Damage to the eyes. Increased sensitivity to sunlight.
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Eating food or drinking water with large amounts of creosote may cause: Burning in the mouth and throat Stomach pains
Accidentally eating large amounts of creosote for a short period of time cancause:
Bad skin rash Eye burns Convulsions Kidney or liver problems Unconsciousness or death
For the first aid treatment of SO2 poisoning we should do the following steps:
Avoid direct contact. Carefully cut around clothing that sticks to the skin and remove the
rest of the garment in case of skin burns.
Briefly flush with lukewarm, gently flowing water until the chemicalis removed or reduced in case of skin burns.
Transport victim to an emergency care facility.8.1.2 Fire Hazards
When and where: An explosion can initiate a fire. Self-ignition of moist and high piles biomass feedstock can lead to a fire.
Spontaneous ignition of piles of biomass feedstock can result from the heat
accumulation in a relatively large mass where combustion starts deep inside
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the pile. A small amount of biomass feedstock is not likely to lead to self-
heating, but this can occur in huge piles and lead to a fire.
In cases where the maximum allowable temperatures are exceeded. Sparks from hot work (welding, cutting, grinding and sawing) can initiate a
fire.
At the removal of hot ashes, a fire can be initiated. In the case where, the decelerating of the engine occur with the wrong
ignition timing, a very rich mixture can form in the exhaust manifold. This
mixture is hot enough to self-ignite, if the amount of air is enough to support
the ignition. If the timing is too late a backfire through the carburetter mayhappen. If the timing is too early backfiring through the intake valve may
occur, which could burn the intake valve. It is to be noted that with the use
of modern engines using integrated control systems, this is less likely to
happen.
Failure of the anti-backfiring system (valve-, rotary valve system, doublesluice) due to unexpected foreign material, failure in the fuel dosing routines
and apparatus, etc may lead to a fire.
The spillage of flammable liquid could lead to a fire, if an ignition source ispresent.
What happens: Physical injury to human being. Damage or destruction of the buildings. May act as an ignition source for an explosion. Release of toxic fumes.
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Possible reduction measures: Fuel should be stored in a closed container, fire isolated, or in a separate
room or building.
A fire-resistant separation (with a specified fire resistance time) between thefuel storage and the gasifier may be required according to local fire-
protection regulations.
The installation of anti back-firing system at reactor, flare and the air inlet tothe engine may be required according to national regulations. A
humidification system at the ash removal in order to prevent fire hazard
from glowing particles. It is recommended to monitor the temperature in the fuel storage pile. Ample ventilations is recommended, preferably natural ventilation. Fire detection and suppression equipment that meet internationally
recognized technical specifications for the type and amount of flammable
and combustible materials stored at the facility should be used.
Accommodation areas should be protected by distance or by fire walls. The ventilation air intakes should prevent smoke or gas from entering
accommodation areas.
A formal fire-response plan supported by the necessary resources andtraining, including training in the use fire suppression equipment and
evacuation, must be prepared. Procedures may include coordination
activities with local authorities or neighboring facilities.
Fire-extinguishing system like fire extinguishers and/or Sprinkler systemshould be used (Note: Regulations on the construction of the fire protection
system must be coordinated with the pertinent fire-protection expert of the
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licensing public authority). Fixed systems may also include foam
extinguishers and automatic or manually operated fire-protection systems.
All fire systems should be located in a safe area of the facility, protectedfrom the fire by distance or by fire walls. The detection equipment specified
needs to be suitable for use in a dusty environment to prevent false alarms or
accidental discharge.
8.1.3 Analysis of Product and Process Safety
In the early stages of process development, the detail of the process has not
been established, but qualitative assessments of major hazards can be made by
collecting information from the material safety data sheet (MSDS) forms for the
chemicals involved. Once a conceptual flow scheme has been developed, semi
quantitative methods such as failure-mode effect analysis (FMEA) and systematic
procedures for identifying hazards such as hazard analysis (HAZAN) can be
applied. An initial pollution prevention analysis can be made if the major process
effluents are known. When the process P & I diagram (Piping & Instrumentation)
has been established and a full mass and energy balance has been completed, then
a full hazard and operability study (HAZOP) can be carried out, and the operating
and emergency procedures can be updated. Safety checklists are often completed at
this stage and then updated and amended at subsequent stages. During detailed
design and procurement, vendor information on instrument reliability becomes
available. This information can be used to make a more quantitative analysis of
likely failure rates, and hence determine whether duplicate or backup systems areneeded. When the plant begins operation, any changes or modifications made
during commissioning or in operation must also go through a detailed hazard
analysis.
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Hazard and Operability studies (HAZOP)A formal operability study is the systematic study of the design, vessel by
vessel and line by line, using guide words to help generate thought about the
way deviations from the intended operating conditions can cause hazardous
situations.
Table 8.1 guide words
Guide Words Meanings Comments
NO or NOT The complete negation
of these intentions
No part of the
intentions is achieved,
but nothing else
happens.
MORE
LESS
Quantitative increases
or decreases
These refer to
quantities and
properties such as flow
rates and temperatures,
as well as activities
like HEAT and
REACT.
AS WELL AS A qualitative increase
(Something in addition
to the design intention,
such as impurities, side
reactions, ingress of
All the design and
operating intentions
are achieved together
with some additional
activity.
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air, extra phases
present).
PART OF A qualitative decrease
(Something missing,
only part of the
intention realized, such
as the change in
composition of a
stream, a missing
component).
Only some of the
intentions are
achieved; some are
not.
REVERSE The logical opposite of
the intention
This is mostly
applicable to activities,
for example, reverse
flow or chemical
reaction. It can also be
applied to substances,
e.g., POISON
instead of
ANTIDOTE or
D instead of L
optical isomers.
OTHER THAN Complete substitution
(It covers all
conceivable situations
other than that
No part of the original
intention is achieved.
Something quite
different happens.
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intended, such as
startup, shutdown,
maintenance, catalyst
regeneration and
charging, failure of
plant services).
Safety checklistsA safety checklist, covering the main items that should be considered in process
design should include materials, process, control systems, storages, fire protection
system and others.
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8.2 Environmental Consideration
With growing evidence of global warming, the need to reduce human-made
greenhouse gas emissions is being recognized. Emission of other air pollutants,
such as NO2, SO2, and Hg, is no longer acceptable, as it was in the past. In
elementary schools and in corporate boardrooms, the environment is a major issue,
and it has been a major driver for gasification for energy production.
Biomass has a special appeal in this regard, as it makes no net contribution
to carbon dioxide emission to the atmosphere. Regulations for making biomass
economically viable are in place in many countries. For example, if biomass
replaces fossil fuel in a plant, that plant earns credits for CO2 reduction equivalent
to what the fossil fuel was emitting. These credits can be sold on the market for
additional revenue in countries where such trades are in practice.
8.2.1 Carbon Dioxide Emission
When burned, biomass releases the CO2 it absorbed from the atmosphere in
the recent past, not millions of years ago, as with fossil fuel. The net addition of
CO2 to the atmosphere through biomass combustion is thus considered to be zero.
Even if the fuel is not carbon-neutral biomass, CO2 emissions from the gasification
of the fuel are slightly less than those from its combustion on a unit heat release
basis. Sequestration of CO2 is becoming an important requirement for new power
plants. On that note, a gasification-based power plant has an advantage over a
conventional combustion-based PC power plant
8.2.2 Sulfur Removal
Most virgin or fresh biomass contains little to no sulfur. Biomass-derived
feedstock such as municipal solid waste (MSW) or sewage sludge does contain
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sulfur, which requires limestone for the capture of it. Interestingly, such derived
feedstock also contains small amounts of calcium, which intrinsically aids sulfur
capture.
Gasification from coal or oil has an edge over combustion in certain
situations. In combustion systems, sulfur in the fuel appears as SO2, which is
relatively difficult to remove from the flue gas without adding an external sorbent.
In a typical gasification process 93 to 96% of the sulfur appears as H2S with the
remaining as COS (Higman and van der Burgt, 2008, p. 351). We can easily
extract sulfur from H2S by absorption. Furthermore, in a gasification plant we can
extract it as elemental sulfur, thus adding a valuable by-product for the plant.
8.2.3 Nitrogen Removal
A combustion system firing fossil fuels can oxidize the nitrogen in fuel and
in air into NO, the acid rain precursor, or into N2O, a greenhouse gas. Both are
difficult to remove. In a gasification system, nitrogen appears as either N 2 or NH3,
which is removed relatively easily in the syngas-cleaning stage. Nitrous oxide
emission results from the oxidation of fuel nitrogen alone.
Measurement in a biomass combustion system showed a very low level of
N2O emission (Van Loo and Koppejan, 2008, p. 295).
8.2.4 Dust and Other Hazardous Gases
Highly toxic pollutants like dioxin and furan, which can be released in a
combustion system, are not likely to form in an oxygen-starved gasifier. (This
observation is disputed by some.) Particulate in the syngas is also reduced
significantly by multiple gas cleanup systems, including a primary cyclone,
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scrubbers and gas cooling. These reduce the particulate emissions by one to two
orders of magnitude (Rezaiyan and Cheremisinoff, 2005, p. 15).
8.3 Plant location and site selection
Site selection for chemical process plants is influenced by many factors; the
following are the principal factor considered by SINNOT (2003).
8.3.1 Marketing area
For materials that are produced in bulk quantities, where the cost of the
transport is a significant fraction of the sales price, the plant should be located
closed to primary market.
8.3.2 Raw-material
The availability and price of suitable raw material will often determine the
site location.
8.3.3 Transport
The transport of materials and products to and from the plant will be an
overriding consideration in site selection. If practicable, a site should be selected
that is closed to at least two major forms of transport like road, rail, and waterway.
8.3.4 Availability of labor
Labor will be needed for construction of the plant and its operation. Skilled
construction workers will usually be brought in from outside the site area, but there
should be an adequate pool of unskilled labor nearby.
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8.3.5 Utilities
Chemical processes consistently require large quantities of water for cooling
and general processes used, and the plant must locate near a source of water of
suitable quality.
8.3.6 Effluent Disposal
All industrial processes produce waste product, and full consideration must
be given to the difficulties of their disposal.
8.3.7 Local community consideration
The proposed plant must fit in with and be acceptable to the local
community; the local community must be able to provide adequate facilities for the
plant personnel school, housing, etc.
8.3.8 Land
Sufficient suitable land must be available for the proposed plant and for
future expansion. The land should ideally be flat, well drained and have a well load
bearing characteristics.
8.3.9 Climate
Adverse climatic conditions at a site will increase costs. Up normally low
temperatures will require the provision of additional insulation and special heating
for equipment and pipes run. Stronger structures will be needed at location subject
to high winds.
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8.3.10 Political and Strategic consideration
Capital grants, tax concessions and other inducement often given by
government to direct new investments can be an overriding consideration in
selecting the preferred site location.
The proposed plant location is near the waste dump in Khartoum.
Justifications for the selection:
The raw material is available from the waste dump. Minimization of transportation cost of raw material. The proposed location is connected to the high way and rail way. Environmental conditions are taken on consideration in this area. Far from population area.
8.4 Plant layout
The configuration of departments, work centers, and equipment, with
particular emphasis on movement of work (materials and employees) through the
system, has an important role on the process economic, efficiency, and safety. The
ancillary buildings and services required on a site, in addition to the main
processing units (buildings), include:
Storage for raw materials and products. Maintenance workshops. Stores, for maintenance and operating supplies. Laboratories. Fire stations and other emergency services. Utilities: steam boilers, compressed air, power generation, refrigeration,
transformer stations.
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Effluent disposal plant: waste water treatment, solid and or liquid wastecollection.
Offices for general administration. Canteens and other amenity buildings, such as medical centers. Parking lots.
When roughing out a preliminary site layout, the process units will normally
be sited first and arranged to give smooth flow of material through them, units are
normally spaced at least 30m apart, or more for hazardous processes. The location
of the principle ancillary should then be decided.
They should be arranged so as to minimize the time spent by personnel in
traveling between buildings. Administration offices and laboratories, in which a
relatively large number of people will be working, should be located well away
from potentially hazardous processes. Control rooms will normally be located
adjacently to the process unit, but with potentially hazardous processes may have
to be sited at a far distance.
Utility building should be sited to give the most economical run of pipes to
and from process unit. The main storage areas should be placed between the
loading and unloading facilities and the processing unit they serve.
8.4.1 General principles
Plant layout is often a compromise between a numbers of factors such as:
The need to keep distances for transfer of materials between plant/storage
units to a minimum to reduce costs and risks;
The geographical limitations of the site;
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Interaction with existing or planned facilities on site such as existing
roadways, drainage and utilities routings;
Interaction with other plants on site;
The need for plant operability and maintainability;
The need to locate hazardous materials facilities as far as possible from site
boundaries and people living in the local neighborhood;
The need to prevent confinement where release of flammable substances
may occur;
The need to provide access for emergency services;
The need to provide emergency escape routes for on-site personnel;
The need to provide acceptable working conditions for operators.
From the above guidelines the following layout had been prepared.
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Figure 8.1 plant layout
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Reference
1- R. K. SINNOTT, Coulson and Richardson, Chemical Engineering volume 6,Fourth edition, 2005.
2- EPA. 2004. Environmental Protection Agency, Washington, DC. Web site:http://www.epa.gov.
3- Handbook of biomass downdraft gasifier engine system, solar energyresearch institute, U.S department of energy, 1988.
4- Prabir Basu, Biomass Gasification and Pyrolysis Practical Design andTheory, Elsevier Inc., 2010.
5- Ke Liu,Hydrogen and Syngas Production and Purification Technologies, AJohn Wiley & Sons, Inc.,2010.