- For every 10-degree drop in feedwater temperature, a boiler loses 1% in efficiency
- Place drip pockets at least every 300 linear feet in the main steam header to capture condensate
- The higher the pressure, the smaller the condensate pipe size needed, while maintaining proper velocity
For every 10-degree drop in feedwater temperature, a boiler system loses 1% in efficiency, which is why returning as much hot condensate to the boiler feed tank as possible helps to maximize operational efficiency and minimize fuel costs. In addition to reducing costs, a properly designed condensate return system can improve the reliability of equipment in the boiler room.
Consider the way steam is applied to a boiler system. In both heating (using a steam-to-water heat exchanger) and process loads, steam gives up its latent energy and condensate liquid is formed. It all begins in the main steam header, where it is important that properly sized drip pockets be placed at least every 300 linear feet to capture and trap this “liquid gold,” sending it to a condensate pumping station for transport to the boiler feed tank. This may involve the use of several condensate transport stations located throughout the facility.
The other place where condensate is found is at the various users, be it a heat exchanger, jacketed kettle, unit heater, corrugator, etc. It is here where properly selected and sized traps capture the condensate and also assist the air vents in the removal of this troublesome gas. If the gas is not removed from the system, it will cause corrosion and partial pressure problems, which affects the reliability of the process and possibly causes product losses.
To properly capture and transport condensate, there are several important points to know.
A steam trap is a small system that typically consists of the trap, isolation valves, the strainer before the trap and the check valve on the discharge side of the trap.
Condensate needs to be pumped back to the boiler room after it is gathered. One of the key factors to take into account is the velocity of this fluid in the pipe, which will be determined by:
• the boiler’s operating pressure,
• the amount of condensate being trapped,
• pressure at the respective trap’s inlet,
• the resultant pressure in the condensate line,
• the condensate pipe diameter and
• the allowable pressure drop, which should not exceed 20% of the boiler’s maximum operating pressure.
Condensate piping is similar to steam distribution piping in that the higher the pressure, the smaller the pipe size while still maintaining the proper velocity in the pipe. For condensate piping, velocity normally ranges anywhere from 3,000 to 12,000 fpm with 3,000 to 7,000 being the preferred range, or lower if larger piping cost is not a factor.
Safety should be a priority in any system, and it definitely plays a role in a condensate return system.
A condensate return line is often bi-phase, meaning there is a combination of steam and water in the line. As a result, water hammer is a concern – more specifically thermal water hammer. This type of hammer occurs when steam in the line condenses, forming a void that rapidly and violently fills with the condensate liquid at that point. This results in a sharp pinging sound or a loud chugging sound, the effects of which can weaken the pipe to the point of splitting or cracking and spewing scalding-hot condensate in all directions. Remember, this line is often under pressure.
Countering the problem of thermal water hammer, some people have been successful diagnosing the “hot spot” through thermal imaging and taking corrective action through inline condensate diffusion. Another possibility is to capture the flash steam using a flash tank directly from the source or the user before the condensate enters the common condensate return line. This flash steam can then be used for deaeration purposes or possibly a unit heater provided the supply of flash steam is constant and not modulating.
The best solution in many cases is to use a high-pressure receiver where the condensate, propelled by its own motive force at the source, is sent to the boiler room package, which includes a tank, stand and boiler feed pumps. This high-pressure condensate package then becomes the main feed tank for the boiler and its level is maintained by the accompanying deaerator, automatically supplying deoxygenated water as the system demands.
To learn more, watch the webinar titled Boiler Condensate Return Basics. To locate a Cleaver-Brooks representative near you, visit cleaverbrooks.com.