Ensuring low thermal fluid film temperature is essential in designing the thermal oil heaters. The correct design prevent cracking of the fluid and it means that thermal oil boilers are basically quite different in design compared to steam/water boilers. For instance, where water heaters and steam boilers can be heated using a pool of hot water, the thermal fluid in contrary must be heated by forced circulation ensuring high velocity of the thermal fluid at all time. It is recommended that potential users of a thermal oil heating systems make special efforts in order to ensure that the chosen supplier of the thermal oil system is both skilled and experienced in these fields.
4.3.1. Actual working and design of oil thermal boiler
Thermal oil heaters (also called thermal oil boilers, thermal fluid boilers or hot oil units) are developed and designed especially for demanding process heating operations where no compromise on quality are accepted and where reliability is the key word.
The solutions comprising tt boilers are not based on low purchase price – the heaters are developed to ensure low over-all costs including low maintenance and operational costs.
Consequently the boilers heaters are made of first class material and component, without any compromise on quality. The pressure part is designed as standard between 10 bar and up to 40 bar pressure (although operation often are atmospheric and pressure less).
The heaters for thermal oil (heat transfer fluid) are delivered as complete and fully equipped units with all necessary armatures, instrumentations and safety features.
The oil/gas-fired heaters are made with the internal tube coils of pad certified steel tubes. The thermal oil is heated gradually to the operational temperature during the circulation inside the tube of these tube coils – and the heat is transferred to the thermal oil first as radiant heat in the combustion chamber, where the inner cylindrical tube coil and a flat tube coil forms the chamber wall and the bottom respectively. Consequently refractory concrete is avoided. Secondly the thermal oil is heated further by the combustion gasses (which are hereafter cooled). This is done in the outer convection part, as the gasses pass the space gab between the two tube coils. The thermal design ensures a modest volume of the thermal oil relative to the size of the heater, and this allows unlimited thermal.
4.3.3. Flue Gas Coolers – Economizers
whenever it might not be possible to use electrical heating using electricity from wind power, nuclear power or water power, – the environmental challenge is to use oil and gas-fired solutions, but at the same time to reduce the fuel consumption and thus the emission. In this context the low flue gas temperature is the key word. The heat recovery is done by utilization of the quite large amount flue gas heat recovered in flue gas coolers also known as economizers.
Economizers can be delivered as build-on to the oil or gas-fired heater, for heating external colder fluid e.g. Water. Alternatively the thermal oil heater can be made as a flue gas heat exchanger – a recuperator where the external heat source is hot flue gas.
4.3.4. Heat transfer fluid – thermal oil
the circulating heat transfer fluid, also known as the thermal thermal oil needs to be correct chosen. Compromise on this issue can easily result in huge problems – but economical and with respect to ensure personal safety. It cannot be emphasized strong enough how fatal bad, old and inappropriate thermal oil can be for the thermal fluid heating system.
Use a quality brand of thermal oil and make sure that this fluid correspond how the heating system is operated.
An important maintenance detail is that every 6 – 12 months, a sample should be taken from the system and send to a qualified laboratory.
4.3.5. Horizontal and Vertical Design
4.3.6 Advantages of oil thermal boiler over steam boiler
• High temperatures up to 300°c at atmospheric pressure
• Choice-free set-points of the outgoing thermal oil temperature
• Supreme part-load operations without compromising heating quality
• No equipment for pre-treatment, no chemicals / additives etc.
• No heat loss due to hot condensate and flash steam
• No risk of corrosion in the heater and circuit
• Can be used as for both cooling below 0°c and above 100°c
• Low maintenance costs (no dynamic influences, no leaking)
• Quiet in operation (no steam stroke and flash steam noise)
• Easy to operate (does not require boiler certified staff etc.)
• Fluid sample analyzing that determine the condition of the system
• No risk of freezing damages in cold regions.
• Co2-reduction, heat recovery and other environmental issues-heat recovery – for instance as described above – and other environmental considerations have always been a standard topic , long before these became a official worldwide protocol. A lot of money is available by thinking “green”.
4.3.7 Cost analysis for oil thermal boiler
? Cost of boiler- 10 lakhs
? Cost of maintenance is around-10,000/yr
Life of boiler is 10-12 years. So, eventually the operating cost per year is much lower than that of above 2 types of boiler. From all above data, it is beneficial to use oil thermal boiler because of its long life, better operation at higher temperature and pressure.
4.4 Gas Fired Boiler
Gas fired boiler employs gas like natural gas or LPG for firing. Wood has low combustion efficiency and low calorific value as compared to natural gas. Natural gas has high combustion efficiency and high calorific value so that it gives more heat to water by firing less gas.
Cost of natural gas is higher than wood. Its price is around 60 rupees per liter.