Steam Pressure Reducing Station

Demineralized Water Make-up Pumps and Valves Main and Bypass Steam Pressure Reducing Stations Desuperheating Equipment Valves... 

The downstream pressure-sensing pipe of each valve is connected to a straight section of pipe 10 diameters or 1 meter downstream of the nearest tee, elbow or valve. This sensing line should be pitched down, to drain into the low-pressure line. If it cannot drain when connected to the top of this line it can often be connected instead to the side of the pipe. The pipe between the two control valves must be drained through a steam trap, just as would the foot of any riser downstream of the pressure-reducing station. 

In other cases, flash steam is utilized on equipment, which is completely separated from the high-pressure source. Often the low-pressure demand does not at all times match the availability of the flash steam. A pressure-reducing station is often needed to make up any deficit and a surplus valve is required to vent any flash steam in excess of the amount being condensed. 

The steam delivery system forms a major part of the post-boiler section and includes auxiliaries such as superheaters, attemperators (idesuperheaters), and reheaters, plus components such as the various steam headers, steam valves, distribution pipework, pressure reducing stations, and the like. 

The pickup, transport, and redeposition of corrosion debris and deposits can happen anywhere in steam distribution and condensate return systems and are not confined to any particular boiler plant size or pressure rating. For example, deposit pickup may occur in a superheater with redeposition taking place perhaps in a pressure reducing station, steam trap, or condensate line. The starting point for transport mechanisms is often a combination of BW carryover and condensate line corrosion. 

Pressure-reducing stations, orifice plates, pitot tubes, and steam meters may all suffer from excessive mechanical wear and may therefore malfunction. 

Safety Valve Required to Prelect Reducing Station Discharge Pressure in Cose of Valve Failure. SV-I is Set at Slightly Above Downstream Pressure of Reducing Station,and Protects All Equipment Operating at this Pressure on Steam Header. 

With steam generated at or close to the boiler design pressure it is inevitable that some of the steam-using equipment will have to be supplied at a lower pressure. In some cases the plant items themselves have only been designed to withstand a relatively low pressure. Sometimes a reaction will only proceed when the steam is at a temperature below a certain level or an unwanted reaction will occur above a certain level. For these and similar reasons, steam often is distributed at a relatively high pressure which must then be lowered, close to the point of use. Pressure-reduction stations incorporating pressure-reducing valves are fitted to perform this function. 

A control station employed to reduce high pressure steam to one or more lower pressures, thus rendering the steam suitable for a number of downstream processes. 

Also shown in Figure 23.17 are let-down stations between the steam mains to control the mains pressures via a pressure control system. The let-down stations in Figure 23.17 also have de-superheaters. When steam is let down from a high to a low pressure under adiabatic conditions, the amount of superheat increases. Desuperheating is achieved by the injection of boiler feed-water under temperature control, which evaporates and reduces the superheat. There are two important factors determining the desirable amount of superheat in the steam mains. 

In steam condensers, such as may be found on power stations, the reduced pressure may induce air ingress into the condenser. The oxygen present in the air may represent a corrosion agent. Filming amines may be necessary to control corrosion under these circumstances. Alternatively hydrazine or another volatile oxygen scavenger may be used for oxygen and pH control. 

High-pressure fluidized beds are also used in power-station furnaces in a combined cycle in which the products of combustion from the fluidized bed are used to drive a gas turbine, while a steam-tube boiler in the fluid bed raises steam to drive a steam turbine. This system both increases the efii-ciency of the combustion process and reduces pollution. 

Compressor machines are used to increase the pressure of a gas by mechanically reducing its volume within its case. Air is most frequently compressed, but natural gas, oxygen, and nitrogen are also compressed Positive-displacement, centrifugal, and axial compressors are the three most common types used in process facilities and pipeline stations. They can handle large volumes of gas in relatively small equipment and may have a variety of drives (e.g., elearic motors and steam or gas turbines). 

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