HEAT TRANSFER FEATURE


RECOVER HEAT TO REDUCE ENERGY COSTS AND WASTE


Using purpose-built boiler economisers can aid the recovery of waste heat and improve energy efficiency, says Neil English, managing director, ThermTech


ncreased energy efficiency is a constant challenge for industry, energy prices are rising globally so there is a short term necessity to reduce fuel bills in order to remain competitive. There is also a prescient environmental issue which cannot be ignored. These are two strong arguments why power generation operators and energy consumers operating hot water or steam boilers ‘without’ waste heat recovery systems in place need to act now. Opinions may vary, but the general consensus on global warming is that doing nothing is no longer an option - and if action is not taken now the situation may be irreversible as soon as 2020. A 2016 report produced by respected scientific journal Climate Dynamics* analysing current CO2 global emissions suggests that developed nations need to reverse carbon emissions at the latest by 2030 and other nations by 2050. The process of reducing carbon emissions also frequently involves reducing other forms of pollution at the same time. One of the key areas for potential energy saving in existing systems is waste heat recovery. It is important because by


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Even if you are only concerned about the immediate economics, it still makes a lot of sense. We also frequently see monitoring figures before and after installation, so we know it works.” In an industrial boiler system, heat is


reducing the amount of fuel used to produce heat in a boiler installation, heating efficiency increases, resulting in lower fuel use. This serves both the requirement to increase efficiency and reduce carbon emissions. Boilers have been used in factories for over 100 years, and remain a major energy consumer, generating waste heat from the spent gases used to heat the water. Luke Hall, project manager at heat recovery specialist ThermTech, supports the universal application of boiler economisers: “Using an economiser provides a guaranteed method of reducing fuel usage while providing the same boiler output, typically achieving 4% to 6% fuel saving with a return in investment between 6 to 18 months.


Since every application is different, each


economiser should be built to achieve the best transfer efficiency for the boiler design and the way it operates


usually considered ‘waste’ when it is below 100°C as it can’t be used in main processes for boiling, steam creation or sterilisation. This spent heat could be used for ambient heating of the factory or building, but its use is restricted to colder climates or during colder times of the year in temperate climates, plus, installations to provide this type of heating are often large and costly. A more useful alternative technology is to apply a boiler economiser. Spent heated gases from the outlet or flue of the boiler burner are returned to the inlet of the boiler to pre-warm the in-feed water, thus providing a higher inlet temperature to the boiler. This results in less fuel demand to reach a usable water heat. This technique is often used in modern domestic boilers but is not common for industry. Many industrial boiler systems are often older installations and awareness of this energy efficient technique as a retrofit option is not always known, therefore energy savings are looked for elsewhere. Installed between the boiler outlet and


*Climate Dynamics is a peer-reviewed scientific journal published by Springer Science & Business Media


BUDGET-FRIENDLY RO CLEANS UP STEAM PRODUCTION


CFB Boilers has launched a budget-friendly reverse osmosis unit, the BoilerRO, which is capable of achieving almost 100% purity of boiler feedwater for superior quality steam. The BoilerRO is said to cost around half that of many comparable units, making reverse osmosis accessible to steam boiler users that may previously have found the technology price-prohibitive. The unit is suitable for commercial and industrial applications, including those within the medical, pharmaceutical, food and beverage industries. The use of reverse osmosis water treatment results in efficient boiler running capacity due to the optimisation of boiler TDS, and energy savings from less frequent boiler blowdowns. Further benefits of the BoilerRO include superior water taste and clarity, spot-free rinses, and reduced scale. Construction-wise, the BoilerRO offers a number of features usually only associated


with high-end units, such as a stainless steel chassis, three-membrane housing, high pressure pump, and high performance Polyamide 8040 membrane. A compact, vertical design means that it is easy to site, even in awkward locations. The BoilerRO has an estimated production (with public water supply) of ±5,000 – 20,000l/h. CFB Boilers


www.steamboilers.co.uk


the flue or chimney, economisers operate on the principle of heat exchange, salvaging boiler gases to pre-heat the boiler in-feed water. This reduces the energy required to heat the boiler feed water to operating temperature. Usually constructed from carbon steel, the economiser design incorporates finned tubes containing the boiler feed water running perpendicular to the flow of hot outlet gases. By heat transfer the flue gas temperature reduces as it increases the feed water temperature. The extent to which the economiser pre-heats the feed water depends on the design of the economiser and existing boiler parameters. The key to efficient heat transfer rate however is the design of the finned tube surface, which needs to maximise total thermal contact with the hot gas. Since every application is different, each economiser should be purpose built to achieve the best transfer efficiency for the boiler design and the way it operates. This may include minor changes to an existing design, which is common for more traditional designs based on boilers that operate continuously at maximum flow rates. Modern designs with variable flow- rates however, may require something specifically suited to the application.


ThermTech www.thermtech.co.uk


/ PROCESS&CONTROL PROCESS & CONTROL | JULY/AUGUST 2017 17


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