Desuperheaters

The output from the turbine might be superheated or partially condensed, as is the case in Fig. 6.32. If the exhaust steam is to be used for process heating, ideally it should be close to saturated conditions. If the exhaust steam is significantly superheated, it can be desuperheated by direct injection of boiler feedwater, which vaporizes and cools the steam. However, if saturated steam is fed to a steam main, with significant potential for heat losses from the main, then it is desirable to retain some superheat rather than desuperheat the steam to saturated conditions. If saturated steam is fed to the main, then heat losses will cause excessive condensation in the main, which is not desirable. On the other hand, if the exhaust steam from the turbine is partially condensed, the condensate is separated and the steam used for heating. 

From steam tables, the outlet temperature is 251°C, which is superheated by 67°C. Although steam for process heating is preferred at saturated conditions, it is not desirable in this case to desuperheat by boiler feedwater injection to bring to saturated conditions. If saturated steam is fed to the main, then the heat losses from the main will cause a large amount of condensation in the main, which is undesirable. Hence it is better to feed steam to the main with some superheat to avoid condensation in the main. 

Fig. 31. Steam system of a pulp and paper mill where PRV = pressure reducing valve, DSH = desuperheater, and DA = deaerating. To convert MPa to...

If the reboiler heating medium is condensing steam, provide a desuperheater if the superheat is more than 40-60°F. 

Figure 4. Mass and energy balance for desuperheater system.

The maximum or minimum temperature attainable in a vessel can be limited by properly designed jacket heating systems. If steam heating is used, maximum temperatures can be limited by controlling steam pressure. A steam desuperheater may be needed to avoid excessive temperature of superheated steam from a pressure letdown station. 

BR — Barometric Refrigeration Unit G — Compressor CP — Gar Puller GT— Cooling Tower GV — Conveyor D — Drum or tank DS — Desuperheater... 

DESUPERHEATER LIQUID MIXING EDUCTOR FUME SCRUBBER... 

On this system, the turbine is speed controlled and passes steam, depending on the electrical demand. The bypass-reducing valve with integral desuperheater makes up any deficiency in the steam requirements and creates an exhaust steam pressure control. Alternatively, any surplus steam can be bypassed to a dump condenser, either water or air cooled, and returned to the boiler as clear condensate. 

The selection is dictated by economics governing the initial plant cost versus higher turbine output. Usually, the turbine exhaust steam is designed to be slightly superheated, which is desirable, as it allows for heat loss from the steam with minimum condensate losses. At low loads from the turbine, the degree of superheat can rise sharply, well in excess of the normal design conditions, and for this purpose, desuperheaters are often employed to trim the steam temperature at exhaust. 

The purpose of the main fractionator, or main column (Figure 1 -1 o i, is to desuperheat and recover liquid products from the reactor vapors. The hot product vapors from the reactor flow into the main fractionator near the base. Fractionation is accomplished by condensing and revaporizing hydrocarbon components as the vapor flows upward through trays in the tower. 

The convection-pass section contains heat exchangers such as the convection superheater, reheater, and economizer, which are within the boiler proper. Also within the general area of this section are the attem-perators (desuperheaters). 

To convert a liquid into a fine mist by mechanical means. Attemperator (desuperheater) ... 

Cascade configuration controlling the desuperheater control valve. 

In a desuperheater, water at 2,900 kPa and 40°C is sprayed into a stream of superheated s at 2,800 kPa and 325°C in an amount such that a single stream of saturated-vapor steam at 2,7001 flows from the desuperheater at the rate of 10 kg s 1. Assuming adiabatic operation, what is the flow rate of the water What is AS,nlal for the process What is the irreversible feature of the pr... 

A desuperheater conlrol-syslem can be used to re late the temperature in a centrifugal compressor. Such a system can be used to meet the maximum discharge-temperature of the compressor. 

To solve the problem (Fig. 2), variable amounts of liquid methyl chloride are injected as a fine spray, upstream of the compressor, to control the gas temperature. Liquid methyl chloride from a supply source enters the desuperheater at constant pressure, flows down the jacket and enters the main line through exposed, tangentially drilled ports. 

Figure 2 — Desuperheater injects variable amounts of liquid methyl chloride to control the gas temperature...

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