Encyclopedia of Environmental Science and Engineering, Volume I and II

The main problems found with sulfur sorbents involve

mechanical property degradation and/or loss of sulfur capac-

ity over many sulfidation-regeneration cycles. The sorbents

receiving the most attention are all zinc based. Building on the

Cool Water technology, various zinc titanate formulations and

proprietary materials were developed by the U.S. Department

of Energy (DOE)/Morgantown Energy Technology Center

(METC) and used at Tampa Electric—Swisher et al. (1995).

A hot gas pilot scale desulfurization is currently operating

at METC. It uses a simulated coal gas mixture at volumetric

flow rates of up to 120,000 standard cubic feet per hour and

400 psia and up to 1200°F. Fluidized bed technology is ideal

for reactors that continuously circulate reactive and regen-

erated adsorbent. For further information and updates the

reader is referred to the following publication and the DOE

websites:

http://www.netl.doe.gov/publications/proceedings/96/

96ps/ps_pdf/96ps1_5.pdf, and http://www.netl.doe.gov/

publications/proceedings/02/GasCleaning/1.05paper/pdf

One of the world’s largest coal gasification plants for elec-

tricity generation, a 253 MWe power plant based on the Shell

IGCC process, was built and started-up in Buggenum, in the

Netherlands, in 1994. Since October 2001, the installation has

been owned and operated by NUON Power as a fully com-

mercial electric generating unit. Pulverized coal is gasified at

about 400 psi and 2700°F using pure oxygen rather than air.

Fly ash bearing raw gas exiting the gasifier is passed through

cyclones to remove the larger particles. The remaining fines

are collected in a hot gas ceramic candle filter. The filter treats

about 1 million cubic feet per hour of syngas at about 500°F

and 380 psia. The filter contains tube modules with elements

made from a structure of silicon carbide supporting a porous

Mullite grain membrane with a pore size of about 4 × 10 −4

inch. Future plans include co-gasifying waste materials such

as biomass chicken litter, wood products and sewage sludge.

Further cleanup of the syngas involves removal of acid

gases such as COS, H 2 S and chlorides as well as a process to

recover sulfur (see Fig. 1). Also removal of ammonia com-

pounds is included in the water treatment process.

Sources of non-gasifier solid wastes include sludge from

raw water treatment and spent bauxite catalyst from the

Claus unit, spent cobalt/molybdenum catalyst from the tail

TABLE 3

Typical treated product gas composition. (Adapted from Heitz, 1985 for SCGP-1)

Component % Volume (N 2 Free)

Hydrogen 30

Carbon monoxide 69

Carbon dioxide <0.1

Hydrogen sulfide <0.01

Carbonyl sulfide <0.01

Hydrogen cyanide <0.001

Ammonia <0.001

Hydrogen chloride <0.001

Hydrogen fluoride <0.001

Methane 0.03

Water 0.6

Argon 0.2

TABLE 4

Cool water stack emissions. (adapted from Holt 1988)

HRSG Emissions

(Lbs/Million Btu)

Incinerator

combustion

Pollutant products

U.S. EPA

NSPS

Cool Water

Permits*

Cool Water

Test Results**

NOx 0.60 0.13 0.056 140 ppmv

SO 2 0.24 0.034 0.017 116 ppmv

Particulates 0.03 0.01 0.008 0.18 g/m^3

*^ Cool Water Permit for Low Sulfur Coal Operation (Low sulfur coal is defined in the permit as coal containing

less than 0.7 wt.% sulfur).

**^ 1987 EPA Performance Test Results for SUFCo Coal, Holt (1988).

COAL GASIFICATION PROCESSES 169

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