Steam desuperheater

The heat and mass balances can be derived as expressed in the following equations. Steam temperature and pressure of the inlet steam are given, and the balance equations can be applied to determine the amount of inlet steam and water for a given steam temperature and amount in the downstream header. 

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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. 

Steam Desuperheater Desuperheater is used to saturate superheated steam by using BFW because saturated steam is preferred for proeess use ... 

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. 

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. 

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... 

Temperature control requiring additional heat input is normally controlled by regulating the flow rate of steam to the process heat exchanger. A desuperheater should be installed to prevent steam quality variation from causing heat exchanger fouling due to temperature spikes at constant flow. 

It is a good practice to desuperheat reboiler or stripping steam during startups in order to minimize hot-spot formation and, therefore, material degradation at the base of the column. 

It is just as important to maintain a good control of the bottom liquid level in columns where the bottom feed, stripping steam, or reboiler return nozzle enters through a submerged sparger (Fig. 4.3a). Here the liquid level serves as a desuperheater, and its loss may overheat the column or its internals. One incident was reported (440) where plastic packings melted because this level was lost. 

System = Contents of desuperheater (open, steady state) Superheated steam... 

Dryer steam should be free of superheat. Although the condensate inside the dryer desuperheats the steam, a separate desuperheater is used in some cases. The effect of superheating above 100°C is controversial. 

Condensate heat flow is essentially in the same direction as vapor flow. First, steam condensate and evaporator vapor condensate (the latter also variously referred to as secondary condensate and process condensate) are kept separate. Steam condensate returns to the boilers after exchanging some of its heat with process liquor. Process condensate is used as described in Section 12.4.3.2. In the drawing, condensate from each of the first three effects first passes through exchangers that heat the liquor (not shown) moving from one effect to the next higher. Variations include the use of condensate to preheat evaporator feed and the diversion of some condensate to overhead desuperheaters. As an example, the drawing shows the use of second-effect condensate to desuperheat steam and first-effect vapor. 

Steam condensate is a valuable resource. It has considerable thermal value and some potential uses in the process. However, intensively treated boiler feed water must replace any condensate lost from the system. Accordingly, most plants have systems to capture most of the condensate and return it to the boilers. With steam distributed at several different pressures, it is also possible to allow condensate collected at one pressure to flash down to a lower pressure and in the process form more steam at the lower pressure. Steam is often available at the evaporators well above its condensing pressure, in which case it is worthwhile to install a desuperheater. Condensate is a good source of the coolant. 

To reduce the temperature of the steam, a device is utilized that adds water to the superheated steam. Typically, clean condensate is used as it is important that good quality of water is used to cool the steam. By varying the amount of water added, the temperature can be controlled. If the temperature is lowered to within 10 °C of that of saturated steam, at the actual pressure involved, this unit is called a desuperheater (Figure 15.10). 

The purpose is to develop a steam balance for operational supervision as well as for identification of improvement opportunities in the steam system. Models for boilers, turbines, deaerators (DAs), letdown valves, desuperheaters, and steam flash tanks are discussed in the previous chapter. Historian and distributed control system (DCS) data will be coimected to steam balance so that the steam balance is capable of dynamically balancing the steam and power demands due to process variations, units on or off, and weather change. 

Calculate the steam prices based on enthalpy-based method for the steam system in Figure 17.1, which consists of major components of a complex steam system boilers with deaeration and makeup, back-pressure steam turbine, condensing turbine, process steam demand, steam letdown vale, desuperheater, and so on. The economic data are provided in Table 17.1. 

Use desuperheated 60-90 psig steam to reboil the reclaimer. Check this with a thermometer and pressure gauge. If the steam is not saturated, your condensate supply to the desuperheater is not working. The chemistry of MEA degradation and reclaiming is discussed in detail by Polderman et al.2... 

Because this HP steam is superheated, we can produce more than 1000 kg of saturated steam from it. In order to desuperheat this steam, BFW is added to produce saturated steam at 41.0 barg (h = 2797.6 kJ/kg). See Figure E8.6. 

A desuperheater permits the tenperature of saturated steam entering a heat exchanger to be... 

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