In most industrial boiler rooms, there are often significant energy savings to be made if you look in the right places. And it’s important to ensure that heat energy is capture and recovered - not wasted. Doing this will help a steam user to make the steam generation process as efficient as possible and will contribute to reducing fuel consumption and emissions.
It’s worth considering that with the ever-increasing need for carbon emission reduction and sustainability progression, and with climate policies influencing operations, the boilerhouse could be an area where measurable improvements can be made through relatively low-cost upgrades, and with the additional benefits of cost savings and productivity improvement.
So, where to focus?
The general subject of heat efficiency in the boiler house can be split into three key areas –
The demands on modern boilers and operating facilities are constantly increasing, and insulation takes on several important functions, particularly when temperatures and pressures are high.
Insulation provides efficiency benefits by reducing heat loss. This saves energy and lowers costs, also contributing to reduced emissions.
It also protects against contact, ensuring the safety of employees and surrounding plant components. For employees who are regularly working within the boilerhouse, good insulation is necessary so that the ambient temperature is kept within a tolerable range.
Insulation may seem like a basic area of focus, but it can also be a great place to start for quick efficiency gains.
Raw water (from the water supply) is cold - usually around 21°C, and it must be heated for steam to be generated.
Hot condensate contains most of the energy that was used to heat it in the first place, so it is essential for steam users to capture and reuse that heat energy – this can be done through a condensate return system. The hot condensate can be used to pre-heat the feedwater, which means less fuel is required to heat the cold water, or it may be routed to a heat exchanger to heat another application. Condensate return and reuse is an excellent heat recovery opportunity that no steam using facility should overlook.
Similar to condensate recovery, recovering heat from boiler blowdown can deliver significant energy gains.
Boilers should be continuously blown down at the surface to control the total dissolved solids (TDS) content in the water as the concentration here is the highest. This blowdown water is pressurised, hot and dirty, creating large volumes of flash steam and possible disposal challenges.
Releasing the blowdown water to a flash steam system is an excellent option for energy recovery. Because of the pressure drop that the water is subjected to as it crosses the blowdown valve, a percentage will change to steam which can then be captured and used for another purpose. The most obvious place for the flash steam to be used is in the boiler feedtank, which is usually nearby.
Further useful energy can be recovered from the residual blowdown before discharging it to drain. The most frequently used method is to pass it through a heat exchanger, providing heat to another part of the system. This approach typically cools the residual blowdown to about 20°C and in doing so, the benefit is not only recovering the heat energy in the blowdown effluent, but also cooling the water enough for it to be safely discharged into the drainage system. (The temperature at which effluent may be discharged is limited in most countries so it must be cooled enough to enter the drainage system).
When energy is recovered from the flash steam and the condensate in the ways set out above, approximately 82% of the total energy contained in the original blowdown is normally recovered. In addition, 14% (by mass) of the water has been recovered, making a further contribution to savings.
Our advice is for steam users to talk to experts for support in ensuring the boilerhouse is as efficient as it can be and in identifying any areas where waste of heat energy can be avoided. A specialist engineer will be able to advise on what will give the best ROI, while ensuring constant adherence to boilerhouse safety and regulatory rules.
For more information about efficiency in the boilerhouse contact the GESTRA team.
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