YHA Castleton. Waste Oil Burner SDF Funded Project. Final Report. Contents

Transcription

1 YHA Castleton Waste Oil Burner SDF Funded Project Final Report Contents Introduction Technical and Installation Details The oil Energy Burner Making the oil suitable The installation Installation Diagram Did it Work? Appendix 1 Photos Appendix 2 Test Certificate Appendix 3 Tank Signage

2 Introduction Prior to the start of the project the Youth Hostel at Castleton was teaching, accommodating and feeding 32,000 children per year. Most of these are primary school children from nearby cities, Sheffield, Manchester etc. That number of children eat a lot of food, and specifically eat a lot of chips. Before a debate about healthy eating gets underway it is worth pointing out that when a child is visiting for only a couple of days and one is arranging lots of activity and exercise for them as part of their residential the priority is to ensure they eat enough. Cooking this amount of food for this number of children produced significant quantities of waste cooking oil. At that time the waste oil was collected and taken away from the site for disposal. The plan was to use the waste oil as part of the heating fuel for the hostel site to avoid the need for it to be removed from the site and to replace some of the existing fossil fuel usage. The Oil The cooking oil used was usually sunflower or rapeseed oil. Both are used for cooking. The oil is used for cooking at around degrees centigrade. When new it has a smoke point (the point at which it starts to carbonate and evaporate) of about 240 degrees and a flash point (the temperature at which it will ignite in air) of 332 degrees. As the oil is used these temperatures reduce. The temperature range cycles gradually degrade the oil. Crumbs of food in the oil become suspended carbon particles and micro-particles which lower the smoke point and make the oil smell and taste brackish. There is a distinctive and unpleasant (almost eye-watering) smell to old oil which taints the food. In the typical hostel usage the oil in the fryers would be changed after 6 to 8 heating cycles, a week to a fortnight. This would be around 20 litres per change in the fryers alone, with approximately the same used in general cooking. The Energy Available The initial calculations were based on straightforward conversions of the energy content of the oil. The FSA Rating of the oil was approximately 3700kj per 100g. The conversion sum is as follows. 1 Joule =0.278 x 10(power -3) Watt Hours Therefore 1 Kilojoule = Watt Hours 100grams of oil yields 3700kj = Watt Hours or 1.02 Kwatt hours. This assumes 100% efficiency of course. At a more likely figure of 65-70% efficiency at the boiler 100g of waste oil will yield 0.72Kwatt hours. As the oil burner was set up to replace the existing natural gas heating this would represent a C02 saving of g per Kwh. Each 20litre drum of oil that was recycled and burned would produce roughly 144Kwh of energy and save 64 kg of CO2 entering the atmosphere from fossil fuel sources. There is an additional CO2 saving as the oil no longer has to be collected and removed from the site. There is also a significant cost saving as well due to the reduction in gas purchased.

3 The Burner There were a number of different choices of burner/boiler that could have been used. Vaporising drip feed burners (like old Rayburn/Agas) are often used for waste oil as they are tolerant of high viscosity oil. The oil flow rate can be adjusted to suit heavier oil. They are also available cheaply secondhand and this recycling possibility was appealing. They are prone to clogging however and none in this style come with modern flame failure safety cut outs. They are also not very clean burning and the particulate emissions are higher, soot in the smoke. This leads to more frequent flue cleaning and servicing. The most efficient style of burner is the fan assisted pressure jet. In these the oil is vapourised under pressure (7 bar) and sprayed through a very fine nozzle (0.6mm dia) into a fan assisted airstream and ignited with electrodes. The microscopic droplet size means very efficient and complete combustion takes place. They are also fairly straightforward to maintain and service. The model chosen was the Grant Euroflame 50/70,000 BTU (17 kilowatt model). These are well known, easy to obtain spares and different size nozzles for. This was an important point as there was a probability that some adaptation would be required to make it run effectively. This type of boiler is however designed for use with Class C2 Kerosene, light heating oil. This is a relatively light, low viscosity fuel. It is considerably less viscous than old vegetable oil, this was the basis of the engineering challenge. The Oil Burner installed

4 Making The Oil Suitable In order to make the waste vegetable oil perform like kerosene it needs to be less viscous. C2 kerosene is around 16 centistokes, the unit of viscosity. Waste vegetable oil is also full of bits of food and carbon, this needs to be removed so that the vaporising nozzle does not block. This latter problem is relatively straightforward. A series of filters must be introduced in the oil supply system to ensure that flow is maintained. The series was as follows. The oil is filtered through a large hole 1mm mesh filter when it is transferred into the storage cylinder. This removed the larger particles (chips etc.). The outflow of the tank was fitted with a mesh gauze filter as well of the same size. A 50 micron cartridge filter was then fitted in the supply line followed by a 10 micron filter. The 10 micron filter was set up in a line head similar to the type found in truck diesel supply pipes. This was cheap and had filter cartridges with water drain traps already fitted. In storage suspended water particles settle to the bottom of the tank as the water is more dense than the oil. This can be a problem if water drains are not fitted at the lowest point of the system. Both these filters have removable and replaceable cartridge elements which can be changed if they block. At this stage it wasn t known if this would be a regular occurrence or not. Research into other similar installations tended to give plenty of detail of the filtration set up but not much about the operational reliability. For the record the filters have been changed just once in a year of operation and have not blocked. Each time oil has been added to the storage tank the water drains have been checked and emptied. The oil filter installation

5 The other main design issue was manipulating the viscosity of the oil to make it behave like C2 Kerosene. This was done by preheating the oil. At 60 degrees centigrade vegetable oil has a theoretical viscosity of around centistokes, the same as kerosene. This is the figure for pure oil, it is not particularly exact as the degradation of the oil through the heating cycles of cooking and the addition of impurities (food microparticles, food oils, sugars, water content etc) will vary. The Installation The method of preheating the oil was to use a scrapped central heating header tank retrieved from a skip after a combi boiler installation had rendered it redundant. The calorifying coil in the tank was connected to the existing gas fired hot water circulation system so that when the boiler was turned on, hot water would circulate through the coil and warm the oil up. The adjacent hot water storage tanks maintain water at 60 degrees so the oil tank was brought up to very close to this temperature in practice. The oil burner was connected by a thermostatic control to the gas system it was heating the same water and tanks in effect. When the oil burner fired up it shut the gas boiler off and pre-heated its own oil. In order to comply with oil installation regulations the tank was outside the boiler room building. To ensure the oil flowed through the supply pipes even in cold weather a hot water sleeve was fabricated around the pipes. This was created by running the oil pipe inside a larger 22mm copper pipe which was connected to the water circulation. This ensured that the oil arrived at the filter and burner at close to the optimum temperature. The oil was gravity fed from the tank. A rise of 300mm, the height of a single building block proved to be sufficient to maintain a flow.

6 Installation Diagram

7 Did it work? The simple answer is that it did work. The boiler was started and checked initially with a couple of litres of kerosene, then the waste oil was added. The boiler continued to run exactly the same. The temperature of the oil (hard to check exactly) seems to be sufficient, the filters have not clogged and there is no odour or visible particulate emission. It has now run successfully for a full year, typically for hours per week depending on the oil supply. There is one issue which must be mentioned when appraising the success of this particular installation. Between the time the project initiated and the completion the UK Government produced the Food in Schools Guidelines which recommended reductions in the use of fried and deep fried foods. As a result the hostel produced a significantly reduced amount of waste oil. Collection from other hostel sites has been arranged on occasions when it coincided with other journeys however and the boiler is in regular use. The main effect of the WOB has been as a tool for educating the 30,000 schoolchildren who visit the hostel and highlighting the re-use of waste and the need for energy conservation. Recent increases in gas prices have also improved the economic benefit of the waste oil as a gas replacement fuel. The installation from outside

8 The oil storage tank with pipework detail The oil-burner installed next to the hot water cylinder it supplies.

9 Scanned test certificate

10 The Sign on the tank Cooking that does its own washing up? We have built a boiler that burns our waste cooking oil from the kitchens and uses it to heat the hot water that we use in the dishwasher and showers. It reduces the amount of fossil fuels we use and saves the oil having to be transported away from the site. Here s the science bit The cooking oil is vegetable rapeseed oil. When it has been used in the kitchen, either in the fryers or for general cooking it is full of little particles of cooked food and carbon. To make the oil work in the boiler these particles are removed by a pair of filters. One filters down to 50 microns and one down to 10 microns. The kind of oil the boiler was designed for is much less viscous (thinner and runnier) than the vegetable oil. To tackle this we have designed a tank with a pre-heater loop in it to warm the oil up until it is at about 62 degrees. At this temperature the oil is thinned suitably and it behaves like normal heating oil in the burner nozzles. We built the system using scrap materials wherever possible. The oil tank is an old hot water cylinder found in a skip and the copper pipe was also salvaged. The exhaust is just water and Carbon dioxide which will be reabsorbed when the replacement crop is grown. Disappointingly, the exhaust gases don t smell of chips.

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