Encyclopedia of Environmental Science and Engineering, Volume I and II

168 COAL GASIFICATION PROCESSES

The stack emission values presented in Table 4, as per

Holt’s (1988) review of Cool Water data, are impressively

low for a coal-based plant. Sulfur dioxide in the gases leav-

ing the tail gas incinerator is about one fifth the quantity

leaving in the turbine exhaust stream. The turbine exhaust

did not contain sulfur compounds other than SO 2.

A typical gasification process will generate both solid

and liquid wastes. The solid waste retains the natural impu-

rities inherent in the coal such as heavy metals, chlorides

as well as organic compounds formed by the combustion of

coal in the reactor. Testing, as defined in rules and regula-

tions under Section 3001 of the 1976 Resource Conservation

and Recovery Act RCRA, must be conducted to determine

the nature of the solid waste generated by the gasifica-

tion of the particular coal with the specified process. The

wastewater stream exiting the carbon-ash scrubbers may

contain dissolved and suspended fly ash and unconverted

carbon trapped in the scrubber. The treatment of this process

wastewater for discharge will generate sludge which will

have to be controlled and assessed.

A gasification process may not have any atmospheric

emissions during normal operating conditions. Gases are

processed and recirculated so that the desired discharge from

the system is product gas alone. During upset conditions,

however, venting will occur causing releases of gaseous

wastes.

Sources of non-gasifier liquid wastes which must be

evaluated include blowdown from clarifiers and cooling

towers, drainage from equipment and floor areas, demin-

eralizer wastes and sanitary wastes. Contaminants in these

streams are generally a function of the intake water quality

and any chemical additives.

Coal

Coal Receiving

and Storage

Coal Milling

and Drying

Coal Feed

System

Steam to

Utilization

Steam to

Utilization

High

Temperature

Cooling

Solids

Removal

and Cooling

Acid

Gas

Removal

Acid Gas to

Sulfur Recovery

Water Recycle

Water

Treatment To Biotreater

Product Gas

to Power

Generation

Slag to

Utilization

To

Utilization

Oxygen

Gasifier

Quench Gas

BFW BFW

FIGURE 1 Shell coal gasifi cation process block fl ow diagram for SCGP-1.

TABLE 2

Uses of products, co-products and effluents (from Heitz, 1985)

Product gas Power generation

Steam General steam system

Acid gas Sulfur plant/sulfur sales

Slag and ash Roads, fill, other products

Runoff and stripped Biotreater

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