Tips originally published by ABB – Click Here
Faced with steadily increasing energy bills, today's companies need to use a range of monitoring and targeting techniques to identify and implement energy saving measures. It is estimated that basic housekeeping enables many no- and low-cost savings, which can add up to five percent or more of an industrial energy bill, while more formal energy management schemes can achieve savings of 20 to 30 percent or more, depending on which industrial sector a company operates in.
However sophisticated a company’s planned energy management strategy might be, it starts with one essential realisation – you can’t manage what you can’t measure. For example, steam provides a popular and efficient form of heating throughout industry, as well as in building services, but how can boiler operators be certain that their steam systems are working as efficiently as possible?
Efforts must start in the boiler itself, where operators need to aim for the best possible combustion efficiency.
Most waste heat is lost in the stack gases leaving the furnace. Creating conditions that generate the smallest quantity of flue gas at the lowest possible temperature will boost efficiency. This is because channeling extra air through the process simply carries more heat away in the flue gas. Obviously, hotter flue gas also “steals” more energy than cooler gas, so that a 22oC drop in stack temperature can boost boiler efficiency by one percent.
On the other hand, supplying insufficient air will result in incomplete combustion of the fuel. This leads to fouling of heat transfer surfaces and emissions of soot, smoke and carbon monoxide.
Rapid heat transfer
Heat transfer surfaces must be clean in order to conduct heat efficiently, but fouling can also be a problem on the “wet” side of the boiler. Water quality is the key here, since any solid contaminants can cause a build up of scale, which effectively act as unwanted insulation.
The two main sources of contamination are the feed make-up water and the returning condensate. Condensate returns to the boiler from the condenser, having been cooled using locally sourced, lower quality water. Condensers are notoriously prone to leaks however, so cross contamination is common. Feed water on the other hand, is normally de-ionised, pre-heated, deaerated and chemically treated before it makes it to the boiler. A failure in any one of these processes can lead to contamination problems.
Regular boiler blowdown is the obvious way to control contamination, although dosing the feed with chemicals such as ammonia or hydrazine also stops some chemicals getting that far. Careful, continuous monitoring also plays a vital role in ensuring good long-term boiler chemistry. So what should you look for? Typical parameters include: conductivity, pH, dissolved oxygen, sodium, silica, hydrazine, phosphate, ammonia and chloride.
Steam metering throughout the entire distribution system is crucial for good energy management. Proper metering allows operators to see exactly what’s going on. For example, meters can track the consumption of individual user processes across a site. This enables energy managers to encourage efficiency by introducing separate billing, or target energy saving measures where they will have the most effect. Trend information also enables operators to spot malfunctioning equipment or other problems as they develop.
Accurate metering is the key. Operators need to know the mass of steam moving around the plant, since this equates to the energy flow. Traditional differential pressure meters such as orifice plates require peripheral paraphernalia including differential pressure transmitters and a flow computer to produce mass readings for steam, all of which adds up to a high-maintenance headache.
Top tips checklist
- Make sure you are only generating what you need. Measure the demand and compare it with what the boiler is generating. This will ensure you’re not wasting steam heating up your factory instead of your process, for example
- Optimise the combustion process by monitoring the flue gases. Only careful monitoring allows operators to strike a balance between supplying too much air, which carries heat away up the flue, and insufficient air, resulting in incomplete combustion
- Make sure that boiler duty is at optimum efficiency. For example, don’t use two boilers at 30 percent output if you can run one at 60 to 70 percent output
- Check your instrumentation is up to scratch. Modern instruments are typically more robust and more accurate. They are also easier to maintain, and are less prone to problems such as drift
- If you measure steam or gas, measure the mass flow, not the volume flow. It takes ten times the energy to create 1 m3 of steam at 10 bar than at 1 bar, yet the volume is the same