What are actually the advantages of thermal oil over steam?
For the production or transformation of goods the use of heat is often required. This applies to the baking of bread just as to the production of plastic products, the drying of wood or the heating of presses or chemical reactors.
Besides the direct heating, heat transfer plants for the indirect heating on an industrial scale are used for this where the heat is transferred from a heater by means of a fluid heat transfer medium via piping systems to the heat consumer.
The advantages of this direct heat transfer over the direct heating are multiple. So inter alia several heat consumers can be supplied with one heater, a higher efficiency is achieved at a central heat supply system, there is no explosion hazard on the consumer due to the spatial separation between heater and consumer and the maintenance is less for a central unit than for many individual heaters.
Water (liquid or as vapor) is surely the most known heat transfer medium for the indirect heat transfer, at temperatures exceeding 100 °C, however, the entire heat transfer plant is pressurized. In thermal oil plants (the terms “heat transfer oil plants”, “thermal oil plants”, “hot oil plants” or “thermo oil heating plants” are used synonymously ), however, mineral or synthetic oils are used as heat transfer medium.
These are characterized – contrary to water or steam plants – in particular by the fact that they can supply heat in a very wide temperature range almost without any pressure. It is to stress that a temperature of 350 °C can be reached basically pressure-less with a suitable heat transfer fluid (“thermo oil”). Solely the pressure caused by the circulation pump is to be considered (see figure 'Steam pressure curves').
Depending on the required process temperature, many different thermal oils with the properties optimised for the application can be used. Plants with thermal oils feature less maintenance, no water treatment is needed, can be controlled very precisely in comparison to steam plants – due to low Investment expenditures. For the abovementioned reasons, the thermal oil technology is continually developing new fields of application since centuries.
Application fields of thermal oil plants
The chemical industry is one of the most important industries in Germany. In terms of turnover it is behind the vehicle construction and mechanical engineering just behind the electrical and electronics industry at fourth place, in terms of the persons employed at fifth place. The sector primarily produces intermediate goods for almost all production areas.
In the chemical industry, the availability of process heat in the high temperature range plays an important role. Thermal oil systems, for example, are used for the heating of polymerization plants, poly-condensation plants, for spinning head heating and for manufacturing polyester fibres, but also in the sector of plastic extrusion, the temperature control of kneaders, dryers, suction filters and reactors.
Example: Reactor heating
At H&R AG, a manufacturer of chemical-pharmaceutical specialty products based on crude oil and precision plastic parts in Salzbergen/Germany, reactors serve for the production of highly purified paraffin for medical products. H&R (1.550 employees worldwide, annual turnover of more than 1 billion EURO) disposes of one of the oldest but at the same time most modern lubricant refinery of the world.
Together with heat 11, the company installed a new plant for the heat supply of two high-pressure hydrogenation plants in 2013. In this process, unusual solutions were found. True to its motto “Oil is far too good for burning!” the medium-sized chemical specialist processes crude oil to more than 800 different products.
High value is set on the production plants being always on the latest state of the technology. The reactors newly installed in the course of a production expansion and increase in output of the two hydrogenation plants serve the production of highly purified paraffin and white oils for the pharmaceutical, cosmetics and food industry.
Application field: Energy industry
The energy industry supplies private households and companies in particular with gas and electric power but also with district heating or other fuels. It is facing enormous challenges as part of the energy revolution it is – beside the chemical industry and the agriculture – one of the most important pollutant emitters in the global economy.
Furthermore the Federal Government wants to reduce the greenhouse gas emissions by 40 % in comparison to the year 1990. According to experts this is only possible by disconnecting old coal-fired power plants.
In the energy industry, heat transfer plants are used in many fields: Thermal oil systems for example are used for the heating of crude oil tank farms, for gas processing in gas power stations, in combined biomass heating power plants or in solar thermal power plants.
Waste heat recovery for the generation of electricity
Up to 50 % of the energy used worldwide is lost as waste heat without being used. With thermal oil waste heat boilers, this waste heat – e.g. in combined heat and power units – can very well be used. heat 11 realized already several plants where the heat energy gained in the waste heat boiler serves the heating of an ORC plant.
An ORC plant – with an electrical capacity of 1.200 kilowatt for instance – can supply about 3.000 households with environmentally-friendly produced, CO2 neutral electricity which is generated by the combustion of renewable raw materials. At the same time, the waste heat of the ORC process can be used e.g. for wood drying or for provision of district heating.
Tank farm heating
A complete different area of application in the field of energy industry is the heating of crude oil tank farms. So that the viscous crude oil can be transported at all by means of pumps and pipes (e.g. when loading onto tank ships), the large vessels are heated up with thermal oil heating plants. Since these tank farms are often located on the Arabian Peninsula, special requirements are placed to the plant components that must operate reliably at very high humidity, extreme temperature changes and even during sandstorms.
Solar thermal power plants
The world’s largest thermal oil plants can be found in parabolic trough solar power plants in which the irradiation is focused by parabolic-shaped mirrors onto a vacuum-insulated absorber pipe running along the focal line in which a special heat transfer fluid (thermal oil) flows and is heated up to max. 400 °C.
The heat transfer oil (thermal oil) gives off the thermal energy via heat exchangers (preheater, evaporator, superheater, reheater) to a conventional water/steam circuit driving a turbine with a generator to produce electricity. Projects in this industry realized by heat 11 are e.g. the Spanish power plants “Extresol 3” or “Los Arenales”, for a power plant in Morocco heat 11 recently received the order to supply a heater.
The areas for application for thermal oil plants in the energy industry are manifold. They range from the conventional power generation e.g. in gas power plants to the renewable energies (biomass generation, waste heat recovery, solarthermics). The interface is always the efficient heat transfer system with organic fluids (thermal oils).