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PII Oct-Nov 2013

In the grand scheme of things, heating water or a water based solution doesn’t usually represent the greatest engineering challenge the world has ever seen. Keeping the heated process at a precise temperature adds another dimension, but let’s face it, it’s not rocket science. That said if you want to achieve reliable, repeatable heating with energy efficiency and at a minimum cost, then you need to get the grey matter working a bit harder. Whilst water heating based on the domestically familiar scenario of electrically powered immersion heater elements or a simple gas fired heater may be a simple and effective approach, it can be inefficient depending on the process needs you are trying to meet. Such systems can be inexpensive to install depending on the degree of support plant required, but it is the overall operating cost that will really make the difference as to which design is the correct choice. Direct heating using gas or oil fired burners either mounted under a tank or by immersed tube are other obvious methods that can be applied but this type of system can take a toll on the equipment being heated; in no time at all you may find yourself having to fork out to replace those tanks and burners. And so we come to another familiar form of heating which is often considered when the process has limited heating surface or the temperature is close to or above 100°C; the use of high pressure hot water. There’s no doubt about it, this method is tried, tested and proven to be effective although care still needs to be taken to ensure an adequate heat transfer surface can be installed. So that’s that, problem solved? Well, apart from the high ongoing maintenance costs. Oh, and the potential safety issues faced by having large quantities of water under high pressure. And let’s not forget the ongoing costs of annual inspection and insurance reviews plus the ever present risk of corrosion. A further option is to use a Steam Generator, heating the process using simple, high output, heat exchangers often solves the problem of space due to high heat transfer rate achieved by steam. Modern, fast response Steam Generators are able to deliver steam on demand when already hot or on standby, or within a few minutes if the Generator is cold. Unlike other traditional boilers, Steam Generators do not require extensive buildings or supervision and are easy to operate and maintain. However, where’s there’s water there remains the potential for corrosion and the time demand and cost of annual inspection still remain. So is there a way of combining the benefits of Steam Generators – most notably ease of use, high heat transfer rate and fast response with cost-effective operation – whilst avoiding the use of water as the key heat source? The answer, as many of you will be aware, is yes and it comes in the form of thermal fluid heaters. Advantages in abundance… Using many of the same design elements as the standard hot water heating system we mention above, thermal fluid heating systems offer the best of all worlds for the majority of applications. A thermal fluid system consists of a gas or oil fired heater connected to carbon steel flow and return pipework with a thermal fluid operating as the heat transfer medium rather than water. Different fluids, including a wide range of mineral oils or synthetic based fluids, can be used to meet specific process heating requirements and, in some cases, doubling as the cooling agent as well. Removing water from the system also removes the problems caused by corrosion. Even with the best intents, corrosion will eventually occur where water is present requiring regular maintenance and repair but which can eventually lead to equipment failure or at best, the replacement of major system components. Thermal fluid, on the other hand, does not cause corrosion or scale, requires very little maintenance, is not subject to frost damage and does not need to be kept under pressure so there is no risk of a corrosion based leak of pressurised hot water and no need for annual shutdown inspection, which should please both your health and safety officer and your financial manager! The removal of water from the equation also has another, maybe unexpected, benefit in that thermal fluid is a more environmentally friendly option. What could be more environmentally acceptable than water, you might be thinking. Clean, pure water wins hands down every time, but the water used in heat transfer circuits has to be treated with a chemical oxygen scavenger, sludge By Chris Horsley, Managing Director of Babcock Wanson conditioner and pH control correction. Even when using top-grade, environmentally friendly treatment chemicals that are safe and simple to handle there’s no escaping from the fact of chemical intervention. Thermal fluids do not require any chemical intervention and are more often than not a simple mineral oil that can be recycled. The oil typically lasts up to a decade and, with it being contained in a closed circuit no loss system, the only effluent is the exhaust from the heater. Such a design also makes for great energy efficiency, with thermal fluid heating systems regularly boasting 30% energy savings over steam systems. Whilst on the subject of costs, it should also be noted that not only do thermal fluid heating systems not require equipment for water treatment as we have already seen, but as the systems are packaged as a compact unit, special site work is generally not required. This not only has a major impact on overall cost but can mean the system can be installed close to where the heat is needed further reducing the cost of operation. Lastly, but still an important consideration, is ease of use. With all the other systems we have mentioned, varying degrees of skill and experience are required to operate the system effectively, especially where handling chemicals for water treatment is concerned. A thermal fluid system requires the least expertise. Whilst you wouldn’t go as far as to call it child’s play, operating a thermal fluid heating system is very easy, requiring minimal training and virtually no day to day involvement. The system can even be pre-programmed for specific processes. Babcock Wanson, for example, offer a unique menu driven system to allow companies to create and store up to 50 programmes for a heating / cooling system in a simple and operator friendly manner. Each programme can include a ramp up temperature, process soak period and a ramp cooling profile at the end of a cycle. All the operator is required to do is select the desired programme and press the start button. What could be simpler? So it may not be up there with the greatest engineering challenges of our day but for processes that require a plentiful and reliable supply of heat, selecting the right heat raising system is vital; it’s vital to ensure the heat is there when it’s needed and at the correct temperature, that it’s cost-efficient to install, operate and run and that it has minimal environmental impact. For the large majority of applications, this is best achieved with a thermal fluid heating system. Babcock Wanson Ltd, Borehamwood, Hertfordshire Can be contacted on: Tel: 020 89537111 E-mail: info@babcock-wanson.co.uk Web: www.babcock-wanson.co.uk GETTING INTO HOT WATER Heating water based solutions for maximum reliability at minimum cost Process vessels 34 Process Industry Informe r October-November 2013


PII Oct-Nov 2013
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