Reactor gasification

This minimizes the electricity needed for compression of the product gas and maximizes the concentration of the reactive components, CO and H2. 

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Equipment. Partial-oxidation gasification section equipment in many plants consists essentially of (/) the gasification reactor (2) the waste-heat exchanger for heat recovery from the hot reactor gas or direct quench system (J) the economizer heat exchanger for further heat recovery (4) the carbon removal system for separating carbon from the reactor product gas and (5) the carbon recovery system for recycle of carbon. 

The gasification reactor is a vertical, empty, steel pressure vessel with a refractory lining into which preheated feedstock and steam are introduced premixed with oxygen. Steam-to-oil weight ratio is 0.35 1 the oxygen-to-oil ratio is 1.05 1. 

In pelletizing, the water—carbon slurry is contacted with a low viscosity oil which preferentially wets the soot particles and forms pellets that are screened from the water and homogenized into the oil feed to the gasification reactor (see Size enlargement). 

When the recycle soot in the feedstock is too viscous to be pumped at temperatures below 93°C, the water—carbon slurry is first contacted with naphtha carbon—naphtha agglomerates are removed from the water slurry and mixed with additional naphtha. The resultant carbon—naphtha mixture is combined with the hot gasification feedstock which may be as viscous as deasphalter pitch. The feedstock carbon—naphtha mixture is heated and flashed, and then fed to a naphtha stripper where naphtha is recovered for recycle to the carbon—water separation step. The carbon remains dispersed in the hot feedstock leaving the bottom of the naphtha stripper column and is recycled to the gasification reactor. 

It is not possible, however, to calculate accurately actual gas composition by using the relationships of reactions (27-14) to (27-19) in Table 27-12. Since the gasification of coal always takes place at elevated temperatures, thermal decomposition (pyrolysis) takes place as coal enters the gasification reactor. Reaction (27-15) treats coal as a compound of carbon and hydrogen and postulates its thermal disintegration to produce carbon (coke) ana methane. Reaction (27-21) assumes the stoichiometiy of hydrogasifying part of the carbon to produce methane and carbon. 

Note that the methanation section is the last processing step in the HYGAS pilot plant, and it depends on the steady-state troublefree operation of the preceding steps (the gasification reactor, amine purification, and caustic wash sections for cleanup sulfur removal) before it can be brought on-line. 

A coal gasification reactor operates with particles of 500 pm diameter and density of 1.4 g/cm3. The gas may be assumed to have properties of air at 1,000°F and 30 atm. Determine the range of superficial gas velocity over which the bed is in a fluidized state. 

There are different process configuration concepts where FBs form the heart of the technology for the hydrogen-rich gas production. The following recently developed gasification reactor technology can be especially mentioned in this respect 44... 

Large-scale gasification reactor technology based on EF gasification from (a) General Electric (GE Texaco process) and (b) Conoco-Phillips (E-Gas). (Adapted from Meier, D. Faix, O. Fast pyrolysis A route for energy and chemicals from wood—fluidized vs. ablative pyrolysis. In Wood and Biomass Utilization for the Carbon Uptake, Seoul National University, Seoul, 2005, pp. 55-68.)... 

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. 

As feedstock proceeds through a gasification reactor or gasifier, the following physical, chemical, and thermal processes... 

Gasification (Partial Oxidation), in which the feedstock is converted to syngas in the presence of oxygen and a moderating agent (steam) in a refractory-lined gasification reactor... 

Gasification reactor atmosphere (level of oxygen or air content)... 

While exhaust gas cleanup of non-combustion thermochemical conversion processes may be easier than that associated with direct combustion, proper design of the process and emissions control systems is necessary to ensure that health and safety requirements are met. The output products of pyrolysis and gasification reactors can contain a variety of potential process and air pollutants that must be controlled prior to discharge into the ambient air. These include particulate matter... 

Pore-diffusion resistance Reactions involve solid particle size greater than about 1.6 mm All fast, noncatalytic gas-solid (G/S) reactions such as combustion and gasification Reactors with particle size lower than 100 pm to 0.1 mm Catalytic bubbling fluidized beds (BFB) Slurry reactors... 

An important variant of the Fluid Bed system is under development. This variant eliminates use of air or oxygen in the actual gasifier. Steam and coal are the reactants. Since we know from Table 3 that the reaction of steam with coal is endothermic, a heat source must be provided. Hot solids in the form of char are heated in a combustor and are transferred to the gasification reactor as one these processes. In another, hot alkaline oxides react with the carbon dioxide in the gas to form carbonates. The exothermic reaction of carbonate formation supplies the heat requirements of the steam-carbon reaction. Both of these processes depend on a reactive coal or char to implement the steam-carbon reaction. 

Although the ASPEN process models can be put together to simulate many types of processes, it may still be necessary to use specialized or proprietary models. Such would be the case, perhaps, for a specific type of a coal gasification reactor. 

The coal gasification process is represented by a reactor, to which coal, including ash, water and oxygen are fed. Since the gasification reactor is not part of the balance chosen for this analysis, the question of whether water is fed to the reactor in the form of a liquid or in the form of steam can be disregarded. 

As described above, the model only covers the gasification reactor, the waste heat system and the quench. The effect of the downstream sections on the design will be discussed in item 6. 

Influence of the downstream plants. Up to now, we have regarded the coal gasification reactor with the waste heat recovery system as an isolated unit. In the event that the gas generated is intended to be used as fuel gas, for example in a combined power station, this approach is justified. If, however, the gas is to be used as synthesis gas, the effect of the downstream units must be taken into consideration. In such cases it is necessary to feed the gas to a CO shift conversion unit in order to obtain the C0/H2 ratio required for the synthesis process. Apart from gasification at atmospheric pressure, which requires an intermediate compression step, it has proved advisable to locate the CO shift conversion directly downstream of the gasification section. A stage in which dust particles are removed from the gas is situated between these two units. It is assumed that exergy losses do not occur in this unit. 

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