Utility systems waste heat boiler

The exhaust gases are generally discharged into dust and fume knockdown equipment to avoid contamination of the atmosphere. Gas-cleaning equipment includes cyclones, setthng chambers, scrubbing towers, and electrical precipitators. Heat-recoveiy devices are utilized both within and outside the lain. These result in an increase in lain capacity or a decrease in fuel consumption. Waste-heat boilers, grates, coil systems, and chains are used for this purpose. 

Process Steam Generation. Steam generated in the process sections of the plant may be at the highest plant pressure level or an intermediate level. Also, the process area may have fired boilers, waste heat boilers, or both. There may be crossties between utility and process generated steam levels. Enough controls must be provided to balance far-ranging steam systems and protect the most critical units in the event of boiler feedwater shortage situations. 

While this basic definition of cogeneration efficiency seems straightforward, complications are created by the process steam generated from waste heat recovery that can be used for power generation or process heating and that does not require any fuel to be fired in the utility system. The heat supply can be defined as the sum of the heat from fuel (both in the utility boilers and fired heaters) and steam generation from the waste heat recovery (see Figure 23.44)17 ... 

Both concentrated and dilute waste were sent to a pair of John Zink thermal oxidizers equipped with adjustable venturi scrubbers for removal of particulates prior to stack discharge. Water process waste originating primarily from fermentation sectors was sent to the Carver-Greenfield evaporation system. The evaporator utilized a multistep oil dehydration process and was equipped with a centrifuge, waste heat boiler, and a venturi scrubber. The Clinton Laboratory reported an overall BOD and COD reduction of 90 and 99%, respectively, depending upon the configuration used. 

The utility system has as typical units steam and gas turbines, electric motors, electric generators, fired or waste heat boilers, steam headers at different pressures and auxiliary units (e.g., vacuum condenser, water treater, deaerator), and provides the required electricity, power, and utilities. 

At BASF, flammable solid, pastelike, and liquid residues are combusted in eight furnaces. Each combustion unit consists of a rotary kiln with afterburner chamber and a steam boiler. The superheated 18-bar steam from units 1 to 6 is fed into the BASF plant network. In units 7 and 8, a higher-value steam is generated with an efficiency of ca. 74 % and supplied to a back-pressure turbine, where it is expanded from 43 bar to 5 bar. To utilize the heat of the flue gases between 300 C and 180 C, a waste-heat boiler was installed to raise 5-bar steam. Electric power and 5-bar steam are fed into the respective plant systems (Fig. 113). 

The recoveiy of heat from waste gas in a waste heat boiler involves the combined operation of two processes, however. The drawback is that the waste heat boiler has to be shut down when- ever the kiln is stopped. This must be taken into consideration in the design and operation of the boiler. On the other hand, it should be possible to continue operating the kiln in the event of a fault or shutdown of the heat recoveiy system, without any adverse effects upon the burning process in the kila In my report I want to deal more particnlarly with the recovery of heat from waste gases in waste heat boilers. And I want to point out that a waste heat boiler should be considered only if there is no other possibility of utilizing the heat. 

The outer layers of the onion (the utility system) produce utility waste. The utility waste is products of fuel combustion, waste from the production of boiler feedwater for steam generation, and so on. However, the design of the utility system is closely tied together with the design of the heat exchanger network. Hence, in practice, the three outer layers should be considered as being the source of utility waste. 

The objective of the development reported here is to reduce tradional gas producer technology to commercial practice so that unattended biomass utilization systems under completely automatic control can be available to boiler operators now burning fluid fuels in packaged steam and heat generators. The system is to be designed for maximum gas production with minimum carbon remaining in the ash and zero liquid wastes production. 

A new method of utilization of waste gas heat is provided by precalcining systems with bypass, in which up to 100 per cent of the kiln exit gases can be economically bypassed arrd be utilized in a steam boiler, without reqttiring arty eooling. 

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