COAL GASIFICATION PROCESSES 167
Some of the more important coal gasification processes
include those of Texaco, Shell, Dow & British Lurgi. These
are carried out at high temperature 600 to 3000°F and high
pressure 25 to 80 atmospheres. The most developed process
is Cool Water integrated gasification/combined cycle (IGCC)
described by Holt (1988) and Spencer et al. (1986) which
uses a Texaco gasifier. Makansi (1987) compares the per-
formance of various systems. Important emissions data for
IGCC projects are presented at the end of the current review.
Additional information is presented below on the status
of coal gasification environmental effects. A comparison of
the impacts on water streams of various processes is given
in Table 1.
Pruschek et al. (1995) discusses the removal of pollut-
ants from a coal gasification plant in a more efficient and
economical manner than in previous designs by conserving
energy in the cleaning sections of the plant. A zinc titanate
catalyst is being tested for hot (1000°F) gas cleanup potential
at Tampa Electric’s 260 MW coal gasification power plant in
Lakeland, Fla.
Waste gas emissions are reduced by scrubbing the raw
gases leaving the gasifier in an acid gas removal system
and converting the H 2 S (via a modified Claus process) to
sulfur. Sulfur dioxide is thus drastically reduced in the final
stack emissions. NO x levels are reduced by saturating thegas prior to gas turbine combustion (see Spencer 1986) or
Makansi (1987). Advances in process efficiency are pos-
sible, through the use of a combined cycle configuration
and by reducing gasifier energy losses. Figure 1 illustrates
the Shell Coal gasification process. The product gas would
typically be fired in a combustion turbine followed by an
HRSG and a steam turbine (i.e., combined cycle) to com-
plete the IGCC. Heitz (1985) presented data on end uses of
various gasifier process streams (see Table 2). The analysis
of a typical product gas stream appears in Table 3.
From an economic point of view it is desirable to con-
struct an IGCC in phases, Le et al. (1986). In the typical
scenario the first phase would be installation of simple cycle
gas turbines for peaking power. As of 1989 the maximum
single gas turbine output is about 150 MW. In the second
phase a heat recovery boiler is used to generate steam for
either cogeneration or to power a steam turbine (i.e., ordi-
nary combined cycle). Zaininger Engineering (Lewis, 1988)
indicate that there is an optimum time at which the gasifier
plant could be added as fuel cost/availability would dictate.
Normal combined cycle efficiency can be approximately
50% (LHV) whereas IGCC values range from 37 to 42%.
However, new hot gas cleanup processes (such as limestone
throwaway or metal oxide catalyst) are being developed
which may increase IGCC efficiency to about 48%.TABLE 1
Coal gasification wastewater concentrations (mg/l, unless noted otherwise). (Adapted from Epstein, 1987)ComponentKILnGAS
(Illinois No.
6) Moving
BedLurgi
Dry Ash
(Montana
Rosebud)
Moving BedLurgi
Dry Ash
(High-Sulfur
Eastern Coal
at Sasol)
Moving BedLurgi Dry
Ash (Lignite
at Kosovo)
Moving BedBritish
Gas-Lurgi
Slagger
(Pittsburgh
No. 8)
Moving BedGrand Forks
Slagger
(Lignite)
Moving BedHYGAS
(Illinois No. 6)
Fluidized BedTexaco
(Illinois
No. 6)
Entrained
FlowChemical oxygen
demand
(COD)4100–6100 21,000–
23,00012,000 20,000 20,000 25,400 4050 1100Total organic
carbon (TOC)810–1610 — 3500 6000 — — — —Total phenols 260–660 4200–4400 3800 3000 3000 5100 710 < 1
Cyanides and
thiocynates130–300 8–19 < 3 80 1150 150 30 50Total nitrogen 1200–2300 — — 4300 — 5200 3700 —
Ammonia 840–1700 4000–14,000 7000 3700 3000 — — 2100
Total sulfur 430–1030 — 950 — 700 — — —
Chloride 450–710 40–45 670 — 1500 — — 3500
Total suspended
solids (TSS)150–700 — — — — — — —Total dissolved
solids (TDS)1070–2100 1700–4000 — 2000 7000 — — 2220Oil and grease 25–340 — 50 900 — 300 — 6
pH 8.3–8.8 8–10 9 9 9 — — —
Temp. °F, 100s — 9–12 9–12 9–12 9–12 — 16–18 24–28C003_001_r03.indd 167C003_001_r03.indd 167 11/18/2005 10:16:47 AM11/18/2005 10:16:47 AM