ASME Carbon Steel Coal Fired Steam Boiler Superheater And Reheater

Coal-fired Steam Boiler Superheater And Reheater Carbon Steel In Power Plant

Product Description

Functions and characteristics of superheaters and reheaters

functions of superheaters and reheaters:

Superheaters and reheaters are important parts for the heating surfaces, used to increase steam temperature, aiming to improve steam enthalpy and further to increase the thermal circulation efficiency for power station.

Superheaters work to heat surnatured steam to superheated steam with a certain tempetature. When boiler loads or other working conditions change, it is necessary to make sure superheated steam temperature to be normal, and within allowable range of temperature variation.

From the thermal circulation in power station, the original parameters of pressure and temperature is higher, the thermal efficiency of circulation is better, or the steam humidity of the steam turbine rear is too high, influencing its safety. While the superheaer steam temperature is limited by metal materials, at present, due to limitation of metal materials, superheated temperature for most power station boilers are still within the range of 540-555 dgrees, and to avoid the steam humidity of blade of steam turbine rear too big, thus middle reheating system is applied.

Functions of reheaters are to heat exhaust of steam turbine high pressure cylinder to the reheated temperature which is close or equal to superheated temperature, and then send them to middle pressure cylinder and low pressure to expand and work to increase the dryness of blace of steam turbine rear. Usually, the pressure of reheated steam is one fifth of that of superheated steam. Application of reheating system can increase the thermal efficiency for power stations by 4-5%.

So far in our country, units with capacity over 125mw all apply one time middle reheating system. Double reheating can increase again the thermal efficiency of circulation by 2%, but the system is very complicated, it is not applied for national units, but it is common for large boilers overseas.

Working characteristics of superheaters and reheaters:

To improve the thermal efficiency, the pressure of superheated steam have been increased from superhigh pressure to subcritical and supercritical pressure. But limited by the metal performance, the steam temperature of superheaters and reheates are kept within 540-555 degrees.

Because what flow through tubes of superheaters and reheaters are high temperature steam, the convective heat release transfer coefficient of tube wall to steam is quite small, and heat transfer performance is poor, the cooling capacity of steam to tube wall is low. Meanwhile, to make sure reasonable temperature difference of heat transfer, usually superheaters and reheaters are placed at the areas where smoke temperatures are high, and their working temperature of tube wall is rather high, thus the working environment of superhearters and reheaters are quite bad. Especially reheaters, for reheated steam pressure is low, and their capacity to cool tubes are worse, thus that how to make sure tube metal can be safe working on the long term is an important issue when comes to design and operation of superheaters and reheaters. Diagram 4-1 lists the upper limit of allowable temperatures for common metal used in boilers. To avoid use of higher level of alloy steel, when it comes to design of superheaters and reheaters, used tube metal are almost close to the temperature limits when working. This time, if there is rise of temperature of 10-20 degrees, which also reduces the allowable stress a lot. Therefore, Attention should be paid for the design and running of superheaters and reheaters in aspects below:

1.to make sure the steam temperature stable when running. The variation of steam temperature is supposed to be not over+5- -10 degrees;

2.There needs reliable method to adjust temperatures for superheaters and reheaters when operation conditions changes to some extend to maintain rated steam temperatures.

3. to minimize the thermal deviation between parallel tubes.

Application

use for heating saturated steam, steam temperature could be up to 900 degree C.

Superheater Capacity Upgrades to Increase Power Generation

Send us required technical data, such as steam capacity, presure, required temperature etc. We will design accordingly.

Differences

Superheater is to increase the temperature of the steam above its saturation point.
Reheater is basically a superheater that superheats steam exiting the high-pressure stage of a turbine. The reheated steam is then sent to the low-pressure stage of the turbine. By reheating steam between high-pressure and low-pressure turbine it is possible to increase the electrical efficiency of the power plant cycle beyond 40%.The reheat cycle is used in large power boilers since it is feasible economically only in larger power plants.

Details

All the raw materials will be firstly made pipeline cutting.

It is consisted of a series of bare oil(carbon steel,alloy steel,or durable heat steel) and header and other auxiliaries. TubesΦ32,38,42 and so on,also as the request.

Differences

Workshop

Send us required technical data, such as steam capacity, presure, required temperature etc. We will design accordingly.