A boiler is a vessel where water is continuously vaporized to generate steam by applying heat. To generate steam, Boiler steam temperature should be 100 °C or 212°F.
Generally operators try to control the stream temperature at a rated value to get best possible heat rate as well as to reduce fuel costs. For better thermal efficiency and to avoid unnecessary material and thermal stress on thick walled parts of a boiler and turbine, precise control of steam temperature is mandatory on utility boiler.
The main objective of a boiler design is to obtain the highest efficiency in absorption of heat, along with that generation of pure steam, safe and reliable operation are also intended.
What is Boiler Steam Temperature?
A stability in boiler steam temperature can help in avoiding high temperature which may lead to accidents like boiler tube bursts.
A boiler may face different situations like over temperature, slagging, corrosion of boiler walls etc under variable load conditions. To avoid all these issues boiler operating parameters including boiler steam temperature should be monitored continuously.
With variation in working conditions the steam temperature remains extremely unstable and pre detection of temperature change is quite difficult. One common method adopted for temperature control is spraying of water over the steam in between the first and second stage superheating.
Boiler Steam Temperature Chart
If we consider power plant boilers, the steam temperature control is one of the difficult tasks as it follows a nonlinear characteristic. Long dead time and time lag are the factors which make it more challenging.
Different issues like load on boiler, air flow rate, combine effect of service burners and soot accumulation on boiler tubes influence the steam temperature.
Steam Boiler Operating Temperature
Usually to generate steam by boiling water, at sea level, the temperature maintained in a steam is 212°F or near to this. If the boiler is operated under higher pressure, more the temperature can be.
As the steam produced is separated from boiler water in the boiler steam drum, steam is superheated to get high thermal efficiency of the boiler turbine unit. Now a days modern boilers generally raise the temperature of the steam up to 1000°F or 538°C which is near about the creep point of the steel used for super heater tubing.
If we kept the steam temperature of a boiler at a very high level for a longer duration, then it will hamper the working life of the boiler. Always try to keep the steam temperature at a fixed point to avoid the thermal stresses on boiler and turbine.
Boiler Saturated Steam Temperature
The pressure and temperature of saturated steam are directly associated with one another.
In general, steam boilers are always operated under high pressure, so that a small size boiler can generate a large quantity of steam. As pressurized steam require less space, it can be transferred to the point of application with the help of small diameter pipe lines. This also maintain a correct steam temperature.
Boiler Outlet Steam Temperature
Boilers are designed to operate at all pressure and temperature as per requirement.
When a steam boiler is operated under high pressure, the temperature required is also increased (more than 212 °F). Otherwise, at high elevation above sea level, the temperature of a steam boiler may be a bit lower.
If we consider a commercial boiler of a tall building which operate at a much higher pressures like 20 to 40 psi to force steam to a greater height, for each psi increase in pressure, the boiling point of water will also be increased by about 3 degree F.
Boiler Steam Temperature Control
Different devices and methods are adopted to control the Boiler Steam Temperature.
To control the boiler steam temperature most commonly used device is attemptor or desuperheater. The function of a desuperheater is to spray water over the steam flow to reduce its temperature. Mostly water spray is done in between the first and second stage of superheater.
Different methods like changing the angle at which the burners fire into the furnace, bypassing and recirculation of the flue gas are adopted to manage the steam temperature.
The water sprayed is obtained from pump discharge as well as from an intermediate stage of boiler feed water pump.
Steam temperature is measured at the exit point of boiler, then the position of water spray valve is changed to right deviations from the steam temperature set point.
Boiler Steam Temperature Calculation
When heat is applied to water gradually at atmospheric pressure, temperature increases up to 212°F (100°C), this is the temperature at this particular pressure no phase change of water takes place.After that heat addition does not increase the temperature but water changes into steam.
Breville Dual Boiler Steam Temperature
Breville Dual Boiler is a high grade milk steamer with a capability to adjust the temperature in between 265-285 degree F to get a perfect hotter or cooler milk or coffee. The quality of textured milk is totally depend on steaming temperature.
Breville Dual Boiler consists of two boilers inside the same machine, both of them have their own heating element and can be adjusted separately as per our need.
Marine Boiler Steam Temperature
Marine Boilers are water tube type and able to work at high pressures.The highest pressure water tube boilers can reach temperatures of ~600°C. Typical water tube boilers will generate steam at around 110-150°C.
Sage Dual Boiler Steam Temperature
Dual Boilers consists of two boilers inside the single machine and both of them perform different functions.
One of them set a much higher temperature to function like a steam boiler and the other one set a lower temperature will act as a brew boiler. In Sage Dual Boiler we can adjust the temperature of water which will be suitable for our coffee.
Before wrap up the article we can say Boiler Steam Temperature is one of the important parameters which control various aspects related to boiler’s performance.