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.

hazard and environmental of solid wast treatment plant

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