Combustion gasification processes

ALSTOM s hybrid combustion-gasification process for hydrogen production. 

The thermodynamic combustion/gasification processes involved can be analyzed on the basis of the First Law of Thermodynamics (Heat in = Heat out Material in = Material out) and chemical... 

In this study detailed fault trees with probability and failure rate calculations were generated for the events (1) Fatality due to Explosion, Fire, Toxic Release or Asphyxiation at the Process Development Unit (PDU) Coal Gasification Process and (2) Loss of Availability of the PDU. The fault trees for the PDU were synthesized by Design Sciences, Inc., and then subjected to multiple reviews by Combustion Engineering. The steps involved in hazard identification and evaluation, fault tree generation, probability assessment, and design alteration are presented in the main body of this report. The fault trees, cut sets, failure rate data and unavailability calculations are included as attachments to this report. Although both safety and reliability trees have been constructed for the PDU, the verification and analysis of these trees were not completed as a result of the curtailment of the demonstration plant project. Certain items not completed for the PDU risk and reliability assessment are listed. 

The different processes and their material requirements are reviewed in References 19 and 20, while annual conferences have been held under the auspices of the U.S. Bureau of Standards and other interested bodies since 1976. The processes involved embrace combustion, gasification and liquefaction, each of which presents characteristically different corrosive environments. 

Stoic Also called Foster Wheeler-Stoic and FW-Stoic. A two-stage, nonslagging coal gasification process, operated under atmospheric pressure and using air as the oxidant. Initially developed by Stoic Combustion Limited Pty, South Africa licensed and further developed by Foster Wheeler Corporation, United States. First used in South Africa in 1950 now widely used in Europe, the United States, and South Africa. 

Once a carbonaceous solid or liquid material is converted to a gaseous state, undesirable substances such as sulfur compounds and ash may be removed from the gas. In contrast to combustion processes, which work with excess air, gasification processes operate at substoichiometric conditions with the oxygen supply controlled (generally 35 percent of the... 

Some gasification processes also use indirect heating, avoiding combustion of the feed material in the gasification reactor and avoiding the dilution of the product gas with nitrogen and excess C02. 

Both gasification and combustion processes convert carbonaceous material to gases. Gasification processes operate in the absence of oxygen or with a limited amount of oxygen, while combustion processes operate with excess oxygen. 

Solid by-products of gasification and combustion processes are significantly different. The primary solid by-product of a low-temperature gasification process is char. Char consists of unreacted carbon and the mineral matter present in the gasifier feed. The most important and significant use of char is as a source of activated carbon. 

In contrast to combustion process, which works with excess air, the gasification process works on partial combustion of coal with the oxygen supply controlled (generally 20 to 70% of the amount of 02 theoretically required for complete combustion) such that both heat and a new gaseous fuel are produced as the coal is consumed. In simplest terms, the stoichiometric reactions are as follows ... 

As discussed above, the pyrolysis of biomass at high temperature (>1000 °C) results in the formation of synthesis gas, a valuable mixture of CO and H2. The decomposition of carbohydrate to synthesis gas is an endothermic reaction since the heating value of product is —125% of that of the feedstock (Reaction 1). The reaction becomes nearly thermo-neutral upon burning about 1/4 of the products. Since the thermodynamics favors the combustion of H2 over CO, the gasification reaction resemble the theoretical Reaction (2). Indeed numerous gasification processes feed 02 or air to drive the gasification reaction. 

Similar to the situation with nitrate esters, the two-stage gas-phase reaction resulting from the combustion of ADN occurs due to the reduction of NO to N2, which is reported to be a termolecular reaction. The heat flux transferred back from the preparation zone to the melt layer zone dominates the gasification process occurring in the melt layer zone. 

In Great Britain, the Imperial Chemical Industries, Ltd., has developed a fluidized coal gasification process (32) using combustion of part of the fuel with air to supply the heat necessary for the endothermic steam-carbon reaction. This procedure is divided into three steps carbonization, air-blowing, and steam-blowing. The first and third steps operate with fluidized beds, and the second with a dilute suspension. Powdered coal is fed into the carbonization vessel, where it is heated by combustion of some of the carbonization gases. The powdered char is blown into a feed hopper connected with the air-... 

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