Slagging combustor

In reflecting on the above discussion, it becomes apparent that one cannot completely divorce the predictive techniques employed, from the particular coal burning application. Pulverized coal firing will require a sensitivity to different conditions than stoker firing, or a slagging combustor. Failure to address the specific conditions inherent in each type of firing system will lead to lower resolution in one s predictive abilities than desired. 

A modification of the pulverised coal plant has a combustion chamber in the form of a cyclone. Molten slag is collected on the walls of the chamber and flows downwards and out of the bottom through a specially designed port. The design is generally known as a "slagging combustor" or "cyclone combustor". 

The method of firing (that is stoker, pulverised fuel, or slagging combustor) will also affect the extent of particular chemical reactions because each of these techniques will have different temperature/time characteristics. 

The oxidant preheater, positioned in the convective section and designed to preheat the oxygen-enriched air for the MHD combustor to 922 K, is located after the finishing superheat and reheat sections. Seed is removed from the stack gas by electrostatic precipitation before the gas is emitted to the atmosphere. The recovered seed is recycled by use of the formate process. Alkali carbonates ate separated from potassium sulfate before conversion of potassium sulfate to potassium formate. Sodium carbonate and potassium carbonate are further separated to avoid buildup of sodium in the system by recycling of seed. The slag and fly-ash removed from the HRSR system is assumed to contain 15—17% of potassium as K2O, dissolved in ash and not recoverable. 

Some of the advantages of fluidized beds include flexibiUty in fuel use, easy removal of SO2, reduced NO production due to relatively low combustion temperatures, simplified operation due to reduced slagging, and finally lower costs in meeting environmental regulations compared to the conventional coal burning technologies. Consequently, fluidized-bed combustors are currently under intensive development and industrial size units (up to 150 MW) are commercially available (Fig. 10). 

More efficient coal utilization can be realized with combined power plant cycles. For instance, the post combustion gases of a conventional combustor or an advanced MHD system can be further utilized to drive a gas or steam turbine. However, the sustained durability of downstream turbine or heat exchanger components requires minimal transport of corrosive fuel impurities. Control of mineral-derived impurities is also required for environmental protection. For the special case of open cycle-coal fired MHD systems, the thermodynamic activity of potassium is much higher in the seeded combustion gas (plasma) than in common coal minerals and slags. This results in the loss of plasma seed by slag absorption and is of critical concern to the economic feasibility of MHD. 

Real MHD Channel Slag (Ki). Detailed TMS and KMS studies were made of vapor transport over a high liquidus temperature (a. 1700 K) potassium-enriched coal slag with initial composition as indicated in Table II. This slag sample was obtained by combustion of Illinois No. 6 coal with additional potassium added to the combustor [see ( )[. Note that this slag composition lies between those of the "Eastern" and "Western" coal-types. 

On the basis of experiments carried out using a laboratory size fluid bed combustor it has been demonstrated that, provided certain precautions are taken, crushed slag and other wastes from conventional coal-burning furnaces can, in the mrgority of cases, be burnt with the recovery of worthwhile amounts of energy and with less environmental pollution from SO2 and NO emissions than could result from the combustion of an equivalent amount of coal. The ash produced has a very low carbon content and is granular in form. 

In contrast to the slag, char particles collected in cyclones working with moving grate installations and the cyclone material from fluid bed combustors, although free form volatiles, appear to burn well even at 800 C, which can probably be attributed to their highly porous character and consequently a large effective surface area available for reaction [13 ]. Data for fluidized bed volatile char are included in Table 2. 

It can be concluded that if the process parameters are properly selected and carefully controlled, most conventional furnace waste materials can be burned in a fluidized bed combustor, in a self-supporting process. Augmentation from the addition of small amounts of fresh coal might be required only in exceptional cases, if the proportion of combustibles in the slag was well below the average. 

In option 2, municipal refuse will be size-reduced by a crusher and fed into the converter. Oxygen will be supplied to the converter and municipal refuse will be dried, pyrolyzed and melted at high temperature. Pyrolysis gas will be directly combusted in the combustor, where waste water will be evaporated and oxidized. Energy will be recovered in the form of steam by a waste heat boiler and electric power will be generated. Lime will be applied to absorb hydrogen chloride and sulfur oxides in the flue gas. Slag may be used for the construction of roads, etc.. 

The combustor off-gas corresponds to the throughput to the gas cooler (e.g., waste heat boiler) of a commercial plant. The gas analysis is given in Table VII, The values for the conventional stoker type incinerator are those in the case of large cities in Japan. They are average values with the exception of HC1, which is slightly higher. The amounts of particulate, SOx and HC1 contained in the off-gas of the Dry Process PUROX System are much less than those of the stoker incinerator. The reason is considered to be that the Cl", SO , etc. combine with alkali metals and shift into the slag in the converter. 

The percentage of the total input of each trace metal which was shown to exit with the slag is given in Table IX. This result for the pilot plant is based on analyses of the outgoing streams. The gas stream analysis was obtained at the combustor outlet, which would correspond in a commercial plant to the inlet of the boiler. The gas would, however, be subsequently cleaned in an electrostatic precipitator and the collected particulates recycled to the converter to be turned into the slag in the case of a commercial plant. The estimation for a commercial plant is premised on use of an electrostatic precipitator designed for a commercial plant of which the outlet particulate concentration is 0.1 g/Nm3 dry gas. It is expected that more than 99.7% of the... 

Sulfur Solubility in Slags for Cyclone Coal Combustors... 

This paper will be divided into three parts. First, the selection of slag compositions will be outlined. Second, sulfide capacity measurements of these slags will be discussed. Third, the desulfurizing potential of a slagging, cyclone combustor will be evaluated using these measurements. 

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