NOVEMBER 7986

Fourth Advanced Coal
Gasification Symposium,
Su Zhou, China

THE SHELL COAL
PROCESS

Maarten van der Burgt and
Jaap van Klinken

Maarten van der Burgt and Jaap van
Klinken work in the Synfuels Development
and Commercialisation Department of
Shell Internationale Petroleum
Maatschappij, The Hague, the
Netherlands. Van Klinken is the head of
the Department while van der Burgt is the
group leader responsible for distillate
and biomass upgrading. Both
were previously at the Shell Amsterdam
laboratory.

Published by Group Public Affairs

For further copies, telephone PA registry
(Shell Centre 491 8), or write to

Shell International Petroleum

Company 

London, SE1 7NA

 

The Shell Coal
Gasl?cation Process
(SCGP) is a clean and
efficient process for
converting coal into gas. gas is a
versatile mixture of carbon monoxide and hydrogen
that can be converted into many valuable products:
electricity, natural gas, chemicals and liquid
transportation fuels among them. SCGP is competitive
for all applications because of its simple operation, its
dry feed system and its generation of superheated
steam in the syngas coo/er which give excellent
thermal efficiency.

Summary

 

 

THE SHELL COAL PROCESS

 

 

Background

SCGP has been under development since
1972. A 6 t/d experimental unit, which has
run for over 12,000 hours, was started up
in 1976 in the Shell laboratory in
Amsterdam and this was followed by a
150 t/d pilot plant near Hamburg, which
operated from 1978 to 1983 providing
6100 hours? experience on coal. Currently,
a demonstration unit (SCGP-1) one?fifth
the size of a commercial plant, is under
construction near Houston, in the United
States.

differs the
previous SCGP experimental and pilot
units, as a result of continuing Shell
research atAmsterdam and at Houston.
These differences increase overall
process efficiency and reliability, and
reduce product gas cost.

SCGP process
description

Dried, pulverised coal is fed pneumatically
in a dense, fluidised phase to
diametrically opposed burners in the
gasifier. Oxygen needed for gasification
and steam (if required) are also routed to
the burners. The addition of coal, oxygen
and, perhaps, steam controls the gasifier
operating temperature (Figure 1).

The gasifier is built for an optimum
pressure of 30?40 bar and a temperature
of The operating
temperature is chosen so that the ash in
the coal melts and drops to the bottom to
be removed as slag. The slag, which is an
inert, glass?like material that is essentially
non?leachable, is quenched with water
and the mixture depressurised to ambient
conditions. The gasifier walls are
protected from over?heating by a
tube?wall that draws in heat to generate
high?pressure steam.

The gas formed in the gasifier
is cooled by a recycling process: some of
the gas leaving the cooler is compressed
and recycled to bring down the
temperature ofthe product entering the

 

Figure 1

 

Shell coal gasification process

High pressure

 

 

 

 

 

 

 

 

 

 

 

 

 

As received superheated
coal steam
Oxygen
Milling 
Drying a 'S'yngas Gas .
Pressurizing Gasitier . cooler treatment .- Clean gas

 

 

 

 

 

 

 

 

water

 

 

 



 

Sulphur

 

 

 

 

Non?leachable
slag

Dischargeable
water

 

 

cooler from the gasifier. This cooling also
generates high quality superheated
steam. Ash in the gas is
solidified so that itwill not stickto the walls
ofthe cooler and isthen removed. The
final product gas can be readilytreated to
remove nitrogen (ammonia), sulphur
compounds and hydrogen cyanide.

Complete conversion of any
coal

SCGP can use any coal as feedstock and
carbon conversions of over98% are
achieved in a single pass. The process is
relatively insensitive to coal properties
such as size (run of mine can be used),
caking tendency, moisture, sulphur,
oxygen and ash. SCGP can gasify
efficiently low?rank coals such as lignites.

High unit capacity

SCGP has been developed with careful
thought towards potential economies of
scale. Forfurther commercial plants it will
be possible to design single trains which
can run 2500 t/d of coal or more and still

 

be small enough to be shop?fabricated
and transported by rail or barge.

High thermal efficiency

Approximately 80?83% ofthe energy
present in hard coals is recovered as
gas and another 16?18% as
superheated steam. The latter may be
used to drive the aircompressors in the
oxygen plant, to generate electricity, or for
other purposes.

Clean product gas

SCGP product gas is essentially all
hydrogen and carbon monoxide, except
for a small amount of carbon dioxide,
nitrogen and argon (Figure 2). Only
minute amounts of methane are present.
Higher hydrocarbons, such as naphtha.
phenols and tars, do notsurvive the
gasmer

Environmental acceptability

Sulphur compounds and ammonia are
easily removed from the raw gas to yield a
productthan can be pipelined if desired.

 

 

 

 

 

Figure2

 

SCGP performance
Effect of different feedstocks

 

 

 

 

Dry gas Texas Rheinbraun Illinois W. Virginia Fluid coke
composition Iignite brown coal No.6 (Pittsburgh (tar sands)
volume) seam) 


H2 32-4 28-6 30-5 31-7 223
CO 61 -8 64-5 65-1 64-3 70-9
CO2 4-6 6-1 2-0 2-0 3-7
CH4 
HZS-COS 00-9 0-7 0-9 1-0 0-9
Cold gas 81 78 81 81 80
efficiency*

*Energy recovered from the coal in the gas

 

 

 

 

 

Most of the ash in the coal is transformed
into a vitreous non?leachable solid which
is suitable as a construction material.
Process water can be readily cleaned and
discharged.

Demonstration
plant

The demonstration plant in
Houston will confirm equipment life and
the scale?up information necessary for
commercial design. Environmental design
data for potential commercial feedstocks
will also be acquired. includes
equipment for demonstrating several
process optimisations. These will increase
stream factor and system reliability, and
reduce capital and operating costs.

A final objective for is to move
further along the experience curve, in part
by developing an experienced operating
team and extensive operating know?how,
which will be readilytransferable to the
first commercial plant.

 

At approximately one?fifth the
anticipated initial commercial module
size, is the most efficient route to
commercialisation ofthe process. It is
much less costly to construct and operate
than a full-scale unit and providesthe
opportunity to test process optimisations
more readily. The maximum scale-up
factor of five for any given piece of
equipment is well within Shell capabilities;
the lower limit on size was actually set by a
requirement to demonstrate equipment
and configurations that would be
employed commercially. Many of the

components will require little or no scaling.

The unit will include coal receiving and
preparation facilities, a high?pressure
gasifierwith high?temperature energy
recovery, solids removal, and gas and
watertreating to provide both clean
medium? BTU gas for power generation
and high?value steam. The unit is
scheduled for start?up in thefirst half of
1987.

is designed to gasify feeds
from lignites to bituminous coals. In
principle, other feeds, such as petroleum
coke, could also be gasified. Feeds will
normally be received bytrain or truck and
gasified at rates of about 250 t/d
(as-received Illinois high sulphur coal) to

 

400 t/d (as?received lignite). The unit is
capable of handling feedstocks with up to
35% moisture, 30% ash and 4% sulphur
at design gas production rates.

Treated product gas will contain
approximately 99% hydrogen and
carbon monoxide (nitrogen?free basis),
lessthan 160 sulphur compounds,
and other minortrace components.
Actual nitrogen content in the product
gas will depend on whether nitrogen or
another gas such as recycled product
gas or carbon monoxide is used as coal
feed transport gas.

The Shell Deer Park Manufacturing
Complex was chosen as the SCGP-1
location primarily because it can make
use of the product gas. Also, some of the
utility requirements can be met by existing
facilities.

Oxygen and nitrogen will be
purchased. Slag and fly slag produced
will be used for road building and other
applications, while acid gas will be sent to
the Deer Park Complex sulphur plant.
Stripped effluent and storm waterwill be
sentto the Complex effluenttreating
system.

Slip stream units

The acid gas removal system is
designed to meet very strict environmental
regulations. A gas treating slip stream unit
will be installed and operated as part of
the overall programme. Effluent water slip
stream units will also be Included.
Properly designed slip stream units
operating on product streams
are cost?effective methods of testing
options and acquiring data necessary to
design commercial plants with varying
environmental constraints and product
gas uses.

Participants

Combustion Engineering?s subsidiary
Lummus Crest and the Electric Power
Research Institute (EPRI) arejointly
participating with Shell companies in the
design, construction and operation of
SCGP?1.Lummus Crestwill provide
engineering design and procurement
services. EPRI will provide an electric utility
industry perspective. Shell Internationale
Petroleum, Shell Internationale Research,
Deutsche Shell, Shell Oil and Shell
Development provided the process
design and much ofthe engineering
design information, and will operate and
manage the unit and experimental
programme.

 

THE SHELL COAL PROCESS

 

Process
applications

There are many applications for the gas
produced in SCGP (Figure 3). The reason
is that the gas is very pure and can be
used to make liquid transportation fuels
via Fischer?Tropsch for the
production of hydrogen and chemicals
such as ammonia, methanol; and for
natural gas (methane).
Furthermore, the gas could be used for
direct iron ore reduction and as
medium-BTU fuel gas for industrial and
domestic heating and for electricity
generation.

Electricity can be generated with much
higher efficiency in coal gasification,
combined cycle power stations than

 

conventional coal?fired ones. SCGP is
also a very efficient process for the
production of natural gas.
Waste heat from the methanation step
allows the co?production of electricity.
Thus SCGP is competitive with processes
where large amounts of methane are
generated in the gasifier itself.

While not limiting the scope of the first
few commercial ventures, we believe initial
applications for electric power generation
are most likely. To this end, Shell
companies have become involved in a
number of venture feasibility studies with
utilities. Full?scale designs would be
finalised operation on the
commercial venture coals, with
construction possible soon thereafter.
This could lead to commercial operation
in the early? to mid?19903. is
expected to continue operating to confirm
commercial design for various
applications and commercial coal types.
From there on, a broad commercial
application of SCGP is expected.

 

Figure 3

 

 

 

Markets for coal gasification

 

GASIFI

 

 

CATION

 

 

 

 

 

THE SHELL COAL PROCESS

 

 

Printed in England by Well Hall Press 09763/2m/11.87

 

 

 

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