HP preheaters

The steam cycle is designed with three LP preheaters, condensing steam that is extracted from the LP turbines, and with four HP preheaters, condensing steam from the HP and IP turbines. The reheat pressure is 4.25 MPa, achieving a reheat temperature of 442°C. The design pressure of the deaerator is 0.55 MPa. Four parallel feed-water pumps are foreseen, of which three are needed to provide the mass flow of 1179 kg/s at fiiU power and the fourth one is kept on hot standby. 

In most larger systems, the recovered flash steam is used in a deaerator, while the HR heat exchangers serve as FW preheaters for both HP and LP boiler plants. 

The base price of the MMC-5 unit is 56,200 (1992 dollars). For the thermal oxidizer portion of the MMC-5 unit, maximum daily fuel cost for natural gas would be 60 (1992 dollars), and maximum daily fuel cost for propane would be 95 (1992 dollars). For the catalytic oxidizer portion of the MMC-5 unit, the maximum daily electrical cost would be 22 (1992 dollars), assuming an electric preheater rated for 36 kW at 480 V is used at 240 V. The daily cost to operate the vacuum/compression unit for the MMC-5 is 6 (1992 dollars), assuming a 3-hp electric motor drawing 2.3 kW is used. 

It is the second of these two areas that is of interest in this chapter. Heat is delivered for steam production in many separate stages. Preheat is first supplied to the low-pressure deionized water prior to deaeration. Higher pressure product (HP boiler feedwater) is further preheated to around 100°C for supply to the waste-heat boiler. The waste-heat boiler is then able to vapourize the high-pressure deionized and deaerated water for final delivery to the steam superheater. 

The tail-gas exiting the expander at 290°C is used to preheat the high-pressure (HP) boiler feed water and also the low-pressure (LP) deionized water (prior to deaeration for high-pressure boiler-feed water use). The important design criteria in this exchanger is that the tail gas should not leave the exchanger at less than 65°C, otherwise problems with condensation/corrosion in the stack will result. The dew point of the tail-gas is approximately 17°C. 

For the synthesis of zinc ferrite (ZnFe204) of stoichiometric composition CFD and HPS samples were mixed in an appropriate ratio. From the chemical analysis the Fe/Zn molar ratio of the mixture was 2.18. To override the problem of the coohng effect of volatiles on the plasma (mentioned above), prior to mixing HPS sample was preheated at 300 °C to reduce its volatile (H2O) content. Conditions of the plasma treatments can be seen in Table 3. In order to improve heat transport between the hot gases... 

If the demand for LPS exceeds the amount of exhaust steam available, the PC opens the pressure let-down bypass. FC-1 serves to minimize the bypass flow. If the pressure controller (PC) opens the bypass and the let-down flow rate exceeds the set point of FC-1, the previously inactive (saturated) FC-3 becomes active and starts cutting back the LPS flow to the boiler feedwater preheater and thereby reduces the plant s demand for LPS. This is an energy-efficient response, because the energy recovered from the LPS supplied to the feedwater preheater is less than the energy content of the HP steam that is needed to produce that LPS. 

The ammonia loop is based on the Ammonia Casale axial-radial three-bed converter with internal heat exchangers (13), giving a high conversion. Heat from the ammonia synthesis reaction is used to generate HP steam (14), preheat feed gas (12) and the gas is then cooled and refrigerated to separate ammonia product (15). Unconverted gas is recycled to the syngas compressor (11) and ammonia product chilled... 

Description Fresh feedstock and recycle streams are preheated and cracked in the presence of dilution steam in highly selective PyroCrack furnaces (1). PyroCrack furnaces are optimized with respect to residence time, temperature and pressure profiles for the actual feedstock and the required feedstock flexibility, thus achieving the highest olefin yields. Furnace effluent is cooled in transfer line exchangers (2), generating HP steam, and by direct quenching with oil for liquid feedstocks. 

An eight inch diameter expander, with 150 HP drive, can process preheated, cracked soybean at 60001bs/hr, producing full-fat soy with low levels of urease and trypsin inhibitor. Also, the hot product can pass into a screw-press (after its moisture is allowed to flash to 5-7%). As most of the oil cells have been ruptured by the expander, a screw-press can process the soybean at three times the capacity it would have had with unexpanded soybean. 

Fig. 21 illustrates some examples of the use of the grand composite curve. Fig. 21(A) shows high-pressure (HP) steam and cooling water (CW) used to satisfy the heating and cooling requirements of a grand composite curve. In contrast, Fig. 21(B) shows the hot utility being satisfied by a mixture of HP and low-pressure (LP) steam. Fig. 21(C) shows yet another option in which a flue gas is used to provide the process hot utility. This flue gas could in principle be either that from a furnace or the exhaust from a gas turbine. The fourth option, in Fig. 21(D), shows the hot utility being satisfied by a furnace flue gas, but with cooling being taken up by LP steam generation, by a feedwater preheat and CW.

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