GASIFICATION DEVELOPMENTS
DISCUSSION WITH
DRS. F.J. DENT, D. HEBDEN, AND
L.A. MOIGNARD AT A GAS RESEARCH BOARD LABORATORIES
AT BOURNEMOUTH
The Gas Research Board has continued its work on the hydrogenation of coal in a fixed bed converter, 1’ internal diameter, 9’ bed depth, designed for operation at 50 atmospheres. This is a batch-type unit holding a coal charge of 300 pounds. The hydrogen enters at the top and is heated by an internal electric heater to 650°C. In this hydro-carbonizer the carbonization zone moves down through the coal at a rate of 9 ft./hr. as compared with a rate of 1” per hour in externally heated coke ovens of the conventional type.
It is planned to make the hydrocarbonization process the fist step in continuous gasification process, with the Lurgi process comprising the second step. An outline of the process is shown in figure 4.
The Gas Research Board is planning to accomplish the hydrocarbonization step in a fluidized bed. At present they are working on a very small scale, using a 4” diameter reactor, about 5 feet long, and with a coal charge of 4-1/2 pounds of 25-200 mesh material. They have made only a relatively few tests in this apparatus but they are very enthusiastic about this as the hydrocarbonization step.
Their work on the methane synthesis is well known and has been adequately reported in several of their publications. It was summarized by Dr. Dent as follows: The process operates at a 2,000 hourly space velocity and at 20 atmospheres with a corresponding temperature of 300 to 500°C. The chief problems involved in the development of the process were:
1. Avoidance of carbon deposition.
2. Avoidance of sintering of catalyst.
3. Removal of heat of reaction.
4. Recovery of heat of reaction.
5. Extreme purification of the feed gas.
The carbon deposition problem was minimized by the use of recycled gas and by the use of a relatively high portion of promoter to catalyst (80% alumina, and 20% nickel). If the gas contains more than certain established quantities of CO, it is necessary to use steam in order to avoid the conversion of carbon monoxide to carbon and carbon dioxide. Purification of the gas is done in two stages. Starting with a gas containing 30 grains of organic sulfur per 100 cubic feet, one passage over nickel chromium catalyst at 250°C. results in an outlet gas sulfur concentration of 0.1 to0.2 of a grain per 100 cubic feet. The final purification is done by passage of the gas over basic nickel hydroxide to obtain a purified gas containing 0.01 grain per 100 cubic feet.
The Gas Research Board is interested in studying a fluidized intermittent process for the production of water gas. A very small experimental unit was being constructed. It is planned to fluidize during the blast and the run. The air for the blast will be preheated in a regenerator to 900°C. Similarly, the steam for the run will preheated to 1,000°C. It is planned to run non-slagging with ash being removed by entrainment in the exit gas.
The Bournemouth Gas Undertaking which is in reality the operating company of the Bournemouth Gas Works has been developing a dynamic iron oxide purifier in which the oxide flows countercurrent to the gas. The development work has been done on a unit having a capacity of 1,00,000 cubic feet per day with a bed diameter of 8 feet and a depth of 6 feet. The hourly space velocity in this unit is 100 as compared with a space velocity of 6 for normal day box operation. The oxide is circulated from the purification box to a revivification vessel where it is continuously revivified and returned to the purification box. A Redler conveyor is used for transporting oxide from one vessel to another. The oxide picks up about 1% of its weight of sulfur per pass and can be used without difficulty until it contains as much as 50%, or more, of sulfur. The pressure drop across the experimental unit is 12 inches of water and approximately 1-1/2 to 3 horsepower are required for recirculation of the oxide. It is estimated that the capital cost of this unit will be 1/2 that of the normal dry box, and the system is regarded as being competitive with liquid purification. The commercial development of the unit will be handled by Humphreys and Glascow, Ltd.