Full steam ahead

Spirax Sarco makes some recommendations to minimise the effects of the forthcoming Climate Change Levy.

The recent floods in Britain are seen by many people as a sign of climate change starting to make itself felt – in future, floods could be a regular feature of the UK climate.

To help slow down these changes, next Spring the government will introduce the Climate Change Levy (CCL). This will see energy bills rise, adding around 0.43p per kWh for electricity, 0.15p per kWh for coal and gas, and 0.07p per kWh for LPG for industrial and commercial users.

Based on agreements reached at the Kyoto Summit in 1997, aiming to cut greenhouse gas emissions by 12.5% below the 1990 level by 2010, the CCL is one of the UK government’s mechanisms to help deliver its commitment. The Levy effectively imposes a tax on companies according to their energy consumption – the more energy efficient a company becomes, the lower their resulting tax will be on their energy consumed.

So how can your company minimise the impact of the new tax? One of the first areas to tackle is your boiler blowdown routine, probably one of the least understood areas of boiler operation. When you blow down a boiler, you are literally throwing energy down the drain. To minimise the impact of the CCL, you need to optimise this energy loss. Cost savings can be achieved by improving the control of Total Dissolved Solids (TDS) in the boiler, the dissolved solids in the boiler water that remain when steam is produced which can result in reduced boiler efficiency.

Boiler blowdown produces large quantities of heat that can be easily recovered as flash steam. After it passes through the TDS control valve, the lower pressure water and resulting flash steam flows to a flash recovery vessel where they are separated, the flash steam is then re-used in the heating process. Even greater savings can be made by passing the remaining blowdown water through a heat exchanger to heat the make-up water coming into the boiler feedtank.

Much better is to monitor the boiler’s TDS level and use the minimum amount of blowdown to maintain the highest permissible TDS level. Automatic TDS control measures the actual TDS level and water is drawn off the boiler continuously, but at a varying rate, to maintain a steady TDS level at the optimum allowable value.

The first step is to minimise your TDS blowdown rate, leaving the boiler operator to undertake, at least once per day, bottom blowdown solely for sludge removal. Even at the optimum blowdown rate, you could heat 13 average UK houses with the energy removed from a medium-sized 10,000 kg/hr boiler. With proper heat recovery you can recapture 80% of this energy.

One practice that is commonly overlooked is the return of condensate to the boiler feed tank. Formed by condensed steam, condensate needs to be drained from pipelines and equipment to maximise the use of the high heat content of steam and avoid the risk of waterhammer.

Another benefit is that less fuel is required to produce steam from hot feed water rather than from cold water make-up. Using the returned condensate to raise the boiler feed water temperature by 6 degrees C gives a fuel saving of 1%. Heating in the feed water tank is most effectively achieved by condensate returned through a deareator head, which mixes returned condensate, flash steam and cold make up water as it is fed into the tank.

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