November 2020

30 | Plant & Works Engineering www.pwemag.co.uk November 2020 Energy, the Environment & Water Focus on: Boilers, Burners & Controls PWE takes a look at ways in which businesses can save money on energy bills and reap the rewards in the upcoming months. Invest now and save A s the government makes moves to open businesses and get the country’s workforce off of furlough and back into the work environment, there are many companies for whom the rest of the year – and beyond – will be challenging. There are currently numerous grants and loans available to help businesses through this tricky period. By investing into the business and improving efficiency, the business can reap the rewards in the upcoming months. Where to invest? Depending on your boiler set-up there will be numerous areas which could allow businesses to achieve significant energy savings and substantially reduce outgoings. From reviewing electronic controls, utilising oxygen trim and reviewing air damper performance to investing in inverters and looking into a plant master system, there are many ways in which set-up efficiency can be improved. Energy Technology and Control’s (ETC) industrial burner control experts have suggested a number of ways that investing in your business’ electronic burner controls can reduce your energy bills in the coming months. Linkageless burners A linkageless burner is one with individual stepper motors for each fuel and air function. Linkageless systems have many advantages, while mechanical linkages can have limitations. Regardless of the linkage quality, there will always be some hysteresis – or “drift” – as a result of play in each connection point. Generally, hysteresis increases with the number of connection points and increased hysteresis compromises efficiency. For example, ETC says if a burner is capable of operating at 3% oxygen at a given firing rate, but has multiple connection points from the modulating motor to the fuel – or air – control devices, it is unlikely that these control devices will return to the same position when driven up as they do when driven down. For this reason, an O2 level generally has to be set higher to compensate for this effect. This reduces combustion efficiency and increases fuel costs. Linkageless burners have no backlash. Therefore on a frequently modulating burner, energy savings of up to 1% are common. Increased turndown Boiler turndown ratio is the ratio of maximum heat output to the minimum level of heat output at which the boiler will operate efficiently or controllably. Boilers are often designed to operate at a variety of output levels. When the desired temperature/pressure point is approached, the heat source is progressively reduced. Conversely if pressure/temperature falls, the heat source is progressively turned up. If the application requires a boiler to operate at a low proportion of its maximum output, a high turndown ratio is required. On the contrary, explains ETC, in applications where the operational conditions are not expected to vary significantly (for example, a large power plant), a low turndown ratio will be sufficient. If the power plant is only working at a small fraction of its maximum and the turndown ratio is too low, the burner will still need to be shut off when the desired pressure/temperature is achieved. This leads to a rapid reduction in temperature/pressure, requiring the boiler to restart. This is detrimental, as flue gases are purged during both the shut-down and start-up phases, leading to energy losses and inefficiency. Plus, typical start-up times for boilers are in the order of 1-2 minutes, leading to an inability to respond to sudden load demands. On an electronic burner control, the low fire point can be set lower than the ignition point, this means that the turn-down ratio can be increased. As a result burner on/off cycles and their associated cold air purges also can be reduced, resulting in energy savings. While savings will vary with boiler utilisation, savings of 5% have been reported on a burner that prior to conversion had an on/off frequency of approximately once every 10 minutes. PID control If a plant does not run continuously, then the second internal PID modulation circuit – which electronic fuel:air ratio controls have – can be used to switch the boiler to a lower steam pressure or hot water temperature during periods of reduced activity. Using a second boiler set point according to ETC can provide energy savings of approximately 10% per annum. Fan speed control When using mechanical cam control and basic electronic fuel:air ratio controls, burner engineers, explains ETC, may at times sacrifice combustion efficiency at low fire to achieve an improvement in burner turn-down. Air dampers can leak and even when fully closed the air flow can be substantial. Engineers can work to reduce the fuel valve setting but cannot reduce