One method of improving a plant's energy efficiency is to increase the condensate returned to the boiler. Steam lines supply critical resources to processes, and gas lines supply critical fuel to the boilers to make steam. Condensate return lines are as critical to your facility as the steam or gas lines. When steam transfers its heat in a manufacturing process, heat exchanger or heating coil, it reverts back to a liquid phase called condensate. Condensate return lines capture and recycle this essential energy by bringing the byproduct of steam back to the boiler for recycling to allow reuse of the thermal BTUs previously input as sensible heat, saving resources. Condensate should be treated as a valuable commodity and can be utilized throughout the plant and in most industries.
Returning hot condensate to the boiler makes sense for several reasons. As more condensate is returned, less makeup water is required, saving fuel and chemical treatment costs. Less condensate discharged into a sewer system reduces disposal costs. Return of high-purity condensate also reduces energy losses due to boiler blowdown. Significant fuel savings are realized, as most returned condensate is relatively hot (130-225 degrees Fahrenheit), reducing the amount of cold makeup water (50-70 degrees Fahrenheit) that must be heated. In most cases, condensate should be returned to the boiler room receiver tank as hot as possible.
Condensate can also be utilized at different stages in the plant to increase thermal efficiencies and reduce the costs associated with the generation of steam at the boiler. There are ways to increase system efficiency and capture these generated BTUs before they are sent back to the boiler room to a deaerator or condensate receiver and released into the atmosphere:
Flash high-pressure condensate to regenerate low-pressure steam: Low-pressure steam requirements are usually met by reducing high-pressure steam with a control valve, but a portion of the process requirements can be achieved at lower cost by flashing high-pressure condensate. Flashing is particularly attractive when it is not economically feasible to return the high-pressure condensate to the boiler.
For example, in a plant, saturated steam at 150 pounds per square inch gauge (psig) is generated, a portion of which is reduced to supply 15-psig steam at a process. Assuming continuous operation, the ability to supplement the 15-psig steam needs by flashing 5,000 pounds per hour (lbs/hr) of 150-psig condensate into low-pressure steam is cost effective. When 150-psig condensate is flashed to 15 psig, 12.7 percent of the condensate flashes back into steam, generating approximately 635 lbs/hr of 15 psig steam for immediate use.
Mix condensate flash with high-pressure steam to create medium pressure: Thermo-compressors boost low-pressure steam to higher pressures for reuse in multiple applications. This maximizes energy efficiency by retaining the energy in low-pressure steam while increasing its pressure by mixing in high-pressure steam.
The use of thermo-compressors can fill a demand at high-use locations in the facility. High-pressure condensate return lines can be used by stepping down the pressure and having the condensate that flashes mixed with high-pressure steam to create more medium- or low-pressure steam for use in the system. A thermo-compressor is a simple yet highly energy-efficient piece of equipment.
Directly inject flash into water streams for heating applications: A direct steam-injection heater provides a cost-effective method to heat water and other fluids by injecting steam directly into the fluid. The direct injection heater is designed to handle a wide range of flow rates and deliver hot fluids at precise temperatures using 20-30 percent less energy than an indirect heat exchanger. Direct steam injection can be utilized with continuous supply flash or in batch operations.
Steam and energy conservation can and should be augmented with proper condensate and flash utilization.
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