Pressure reducing and desuperheating system

What is steam pressure reducing and desuperheating system?

 

PRDS, short for pressure reducing and desuperheating system, could achieve both temperature and pressure reduction. It is basically a combination of control valve to reduce pressure, and spray nozzle to lower temperature. PRDS has the same temperature control loop as a desuperheater, only it is added with pressure control loop.

 

Basic uses of steam in industrial application have mainly two jobs: mechanical driving work for rotation equipment and drying & heating medium in process industry. For mechanical driving, superheated steam is preferred, as it is dry steam that doesn’t contain water droplets, which would cause damage to equipment. For drying & heating purpose, saturated steam is preferred due to its higher heat transfer efficiency. Superheated steam extracted from boiler main steam line will go through desuperheating or conditioning to get desired temperature and pressure. That’s where a PRDS is used.

 

Application:

 

1. Protection for downstream equipment like superheater, reheater, turbine in thermal power plant. Superheated steam temperature should keep stable to make sure boiler operation is safe and economic. A lower temperature deviated from design value would weaken thermal efficiency of cycle, while a higher temperature would shorten service life of power plant equipment, or even cause damage like tube failure. For example, steel 12CrMoV could serve 100,000 hours at 585℃ under endurance limit, but it comes to only 30,000 hours at 595℃. Desuperheater in boiler cools down superheated steam and protects downstream equipment from overtemperature.
2. Conditioning for steam discharged from steam turbine bypass system before dumping into condenser.
3. Steam conditioning for district heating.
4. Provide suitable auxiliary steam for heavy fuel oil heating, soot blowing, deaeration, air ejector, gland sealing, etc.
5. Provide a suitable heat transfer medium for exchanger like shell and tube or plate type.
6. Drying & heating & tracing in paper, tobacco, food, textile, refinery, chemical, petrochemical, pharmaceutical, etc.

 

Components

 

A complete PRDS consists of steam conditioning valve, safety valve, pressure transmitter, temperature transmitter, check valve, water control valve, globe valve, strainer, PID controller, etc.

 

Pressure control of PRDS has the similar principle with temperature control. Pressure transmitter gives signal to PID controller, which will then give instruction to pressure reducing valve actuator.

 

PRDS design: split type and combined type

 

For combined PRDS, pressure & temperature reduction happens simultaneously inside steam conditioning valve. This design is featured with much shorter length, compact structure, small footprint.

 

For split PRDS, pressure & temperature control is separated. Pressure reduction happens first inside pressure reducing valve first. It is used for situation like low steam flow where steam conditioning valve is not suitable, or low steam pressure where venturi pipe is necessary to optimize atomizing performance.

 

Why desuperheating is done after pressure reduction?

 

1. Cooling water pressure must be higher than that of steam, so that it could be sprayed into steam flow successfully. If steam pressure is reduced, accordingly, cooling water at a lower pressure is required. It is reasonable from the view of operation cost.
2. After pressure reduction, steam volume expands, that results in a larger pipeline, in which cooling water is easier to disperse and mix. And droplets become more difficult to fall on inner wall.
3. Oppositely, if desuperheating happens first, condensate water will be released from saturation steam after pressure reduction.

 

Supplier

 

As a professional supplier for steam pressure reducing and desuperheating system in China, GeckoInTech are engaged to supply reliable equipment for clients with various requirement. Our products are custom built to give perfect solution to market demand. With more than 30 years experience, we always work harder to take ourselves to next level. Now our desuperheater and PRDS is successfully used in 1000MW unit and exports to Thailand, Indonesia, India, Turkey, Russia, etc.