Fly ash removal

Fly ash may be entrained throughout the incineration system (e.g. in expansion chambers, cyclones or filters). Removal methods for trapped fly ash may differ depending on the cleaning method used with each individual device. 

Collection and storage hoppers should be provided at the bottom of each affected device for removal of batches of the fly ash. The hoppers may be equipped with sliding doors, mechanical trap doors, rotary partitioned devices, Archimedean screws, conveyor vibrators, belt conveyors and other devices. 

A wet method may be used especially when secondary liquid waste treatment facilities are available. Drains should be provided for washing solutions at the bottom of the equipment involved. These drains should be connected to the radioactive liquid waste collection system, or to its equivalent. 

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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. 

Air-pollution control, as in fly-ash removal from power-plant flue gases... 

These remove particles by means of applied electrical forces, and are used extensively on cement and fly ash removal from air streams. The particles are first given an electric charge and are then passed through an electric... 

In order to avoid the unfavorable process conditions, different flue-gas treatment processes for combustion plants based on catalytic filters were developed, which combine fly-ash removal with SCR of ISKh with NH3 [4—8], The advantages of these processes are space and treatment-cost savings, reduced internal and external mass transfer resistances compared to honeycomb SCR catalysts, heat recovery from offgases with good efficiency, and low corrosion problems due to the removal of both dust and NOx at high temperatures. 

Fig. 15.1. Flue-gas treatment by a conventional process comprising a fabric filter for fly-ash removal, a wet scrubber for SO2 reduction and a selective catalytic reduction unit for NOx treatment (from Ref. [4]).

Estimate the flow rate (kg/min and kmol/min) of each component and the composition (mole fractions) of the furnace flue gas. (Ignore the fly ash in calculating mole fractions.) At what rate (kg/min) is fly ash removed from the flue gas by the electrostatic precipitator ... 

As a consulting engineer, you have been contracted to modify an existing control device used in fly ash removal. The federal standards for emissions have been changed to a total numbers basis. Determine if the imit will meet an effluent standard of 10 particles/acf Data for the imit are given below. 

Injection of activated carbon particles into the flue gas to absorb the mercury or operation of the coal combustion to convert a portion of the coal into activated charcoal. The mercuryladen charcoal is then captured by the fly-ash removal system (which may be an electrostatic precipitator. Alter, or dust scrubber). 

Thus, the tendency is to advocate the use of dry lime scrubbing systems thereby producing a waste stream that can be handled by conventional fly ash removal procedures. There are also dry processes, such as the metal oxide processes, in which sulfur dioxide can be removed from gas streams by reaction with a metal oxide. These processes, which are able to operate at high temperatures (approximately dOO C [TSO F]), are suitable for hot gas desulfurization without an energy-wasteful cooUng step. The metal oxides can usually be regenerated by aerial oxidation to convert any metal sulfide(s) back to the oxide(s) or by the use of a mixture of hydrogen and steam. 

Table 2 summarizes the variation in porosity at various stages of treatment of oil fly ash. Acid treatment of oil fly ash removes the most of the inorganic matter from the surface and inside of fly ash particles and produces micro and mesopores. Heating of ash with acid leached out most of the metals in the form of phosphates, sulfates and nitrates. Activation of ash with acid produces more mesopores than raw ash (see Fig. 2). 

Scrubbing Liquor, Power Plant Fluegas 120 49 E E E 7% CaSO , 2% CaSOg. 1% chloride. pH 5.8 6.1. Joy Hi liquid energy limestone scrubbing process for SO and fly ash removal Aeration — extensive Agitation gas and liquid flow Total days — 173... 

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