The transport reactor concept is an advanced gasification power system that meets the future needs of DOE’s
FutureGen program which promotes energy technologies of the future. This system can be used to produce a
combination of the following:
- Electricity
- Synthetic natural gas
- Hydrogen gas stream
The design of the transport reactor allows for a low-capital-cost gasification system that can use state-of-the-art
pollution control systems. The transport reactor development unit was built to facilitate testing at the Power Systems
Development facility in Wilsonville, Alabama. Clients include DOE, M.W. Kellogg, Southern Company Services, the
Electric Power Research Institute, North Dakota Industrial Commission, and many more.
Solids enter the system in a nonpressurized hopper with a capacity of 2500 lb. The coal is gravity-fed into the
pressurized coal lock hopper, which has a capacity of 1700 lb. A set of valves isolates the pressurized lock hopper
from a small, pressurized surge hopper, which maintains an uninterrupted flow of coal while the pressurized coal hopper
is being filled. An auger at the bottom of the surge hopper meters the solids. The rotational speed of the auger is
controlled to produce various feed rates. The feed auger drops the solids into a high-velocity gas stream of ambient
temperature or preheated nitrogen or air (572°F/300°C). The solids can also be augered into the carbonizer rather than
by pneumatic transport.
The TRDU proper consists of a riser section with an expanded mixing section at the bottom, a disengager on top of a
solids standpipe, and a cyclone with its associated dipleg. The solids standpipe is connected to the riser mixing
section by a J-leg transfer line. All of the components in the system are refractory-lined and designed to operate
at 120 psig and an internal temperature of 2000°F (1090°C).
The premixed coal and limestone fed to the transport reactor can be admitted through three nozzles located at various
elevations on the riser. During operation, feed will be admitted through only a single nozzle at a time.
Oxidant is fed to the riser by three pairs of nozzles at differing elevations within the mixing zone. For the combustion
mode of operation, two additional nozzles are provided in the riser to introduce secondary air. Hot solids from the
standpipe are recirculated through the J-leg into the mixing zone, where they come in contact with the oxidant and
steam. This feature prevents exposure of the raw coal to the oxidants, preventing combustion of the volatile matter
released. Only char is burned to provide process heat. This staged gasification process is expected to improve process
efficiency. All gasification, combustion, and desulfurization reactions are carried out in the riser as coal, sorbent,
and oxidant (with steam for gasification) flow up the tube.
The bulk of entrained solids leaving the riser is separated from the gas stream in the disengager and recirculated back
to the riser via the standpipe and J-leg. Gas exiting the disengager is further screened of solids as it enters the
cyclone. Gas exiting the cyclone passes through the hot-gas cleanup loop and proceeds to the gas quench train. Solids
removed by the cyclone are reintroduced to the standpipe and, in turn, to the riser. A solids stream is withdrawn from
the standpipe via a cooling auger system to provide a means of removing accumulated ash and spent sorbents. The rate at
which solids are removed from the system is determined by the level of solids inventory in the standpipe.
The TRDU is fully instrumented with an array of internal thermocouples, pressure and differential pressure transmitters,
and gas flowmeters. All measured process variables are controlled and recorded by a PC-based process control and data
acquisition system.
Gas Quench and Liquid Separation
Gas passes through the sieve tower and then the two water scrubbers. The gas stream enters the bottom of the sieve
tower, where it passes through a series of perforated plates. The plates in the sieve tower are connected for easy
removal for inspection and maintenance. In the sieve tower, recycle oil from the bottom of the tower is cooled and
used to quench the incoming gas. Heat exchangers are used to cool the recycle streams in the sieve tower. The
Dowtherm on the shell side of this heat exchanger can be heated electrically or cooled by passing through the tube
side of a water-cooled heat exchanger, removing heat from the overall system. The tar and oil product is placed in
55-gal barrels for storage and/or analysis. After the sieve tower, the gas enters a direct-contact water scrubber
(venturi cyclone) and is sent to a flare.
Next is a series of two direct-contact water scrubbers (venturi scrubbers/cyclones) that are used when the gas
stream contains minimal amounts of vaporized organic liquids. The gas stream is cooled to between 200° (93°)
and 225°F (107°C) in the first water scrubber and to below 125°F (52°C) in the second scrubber. Heat is removed
from the recirculating water/oil-cooling fluid by a bank of water-cooled tube-and-shell heat exchangers. The gas
from the second venturi is flared, and the liquid products are stored in 55-gal barrels. The flare operates at a
temperature of 1800°F (982°C) and a residence time of 0.5 seconds.
Hot-Gas Filter Vessel
The hot-gas filter vessel (HGFV) is designed to handle all of the gas flow from one TRDU at its expected operating
conditions. The vessel is approximately 48-in. i.d., and 185-in. long and designed to handle gas flows of
approximately 325 scfm at temperatures up to 980°C (1800°F) and pressures of 130 psig. The refractory lining
brings the i.d. down to 28 in., with a 24-in.-i.d. shroud to distribute the airflow. The vessel is sized such that it
could handle candle filters up to 1.5 m long; however, 1-m candles are expected to be utilized in the initial
540°C (1000°F) gasification tests. Candle filters are projected to be 2.375-in. o.d. and with a minimum 4-in. center
line-to-center line spacing.
The following are the design criteria and range of operating conditions for the HGFV:
- Inlet gas temperature: 590°–980°C (1000°–1800°F)
- Operating pressure: 120–150 psig
- Volumetric gas flow: 325 scfm
- Number of candles: 19 (1 or 1.5 m)
- Candle spacing: 4.25 in.
- Filter face velocity: 2.5–10 ft/min
- Particulate loading: <10,000 ppm
- Temperature drop access HGFV: <30°C (50°F)
- Nitrogen backpulse system: unheated
Ports have been added to the filter vessel to allow temperature and pressure measurements to be obtained and for
the insertion of a water-cooled borescope probe for inspecting candle filters online. The ash letdown system
consists of two sets of alternating high-temperature valves, with a cylindrical pressure vessel to act as a lock
hopper. Additionally, a preheat natural gas burner is used to prevent condensation from collecting in the vessel
while the gasifier is starting up.
The nitrogen backpulse system will backpulse up to four sets of four or five candle filters in a time-controlled
sequence. The pulse length and volume of nitrogen displaced into the filter vessel are controlled by the regulated
pressure (up to 900 psig) of the nitrogen reservoir and the solenoid valves used to control the timing of the gas
pulse.
High-Pressure and High-Temperature Sampling System