Modern Waste Heat Recovery Systems for Industrial Plants by Kalugin JSC
One of the most important factors determining efficiency of industrial production is a reasonable use of energy resources. Due to this, companies oriented at energy saving continuously develop and implement programs enhancing energy efficiency of existing facilities. Marina Kalugina, General Director of Kalugin JSC, speaks about instruments which are proposed by Kalugin JSC to solve these tasks.
In the last twenty years Kalugin’s engineers have designed and implemented all-purpose Waste Heat Recovery Systems (WHRS) using heat-exchanging units of various types. These are conventional Tube Recuperators, Heat Pipe (Thermosyphon) Heat-Exchangers which are exclusive for Russia and Plate Heat-Exchangers which have gained widespread currency recently.
These systems have already proved their efficiency in ferrous and non-ferrous metallurgy, they have an enormous potential for use in chemical and petrochemical industries, heat and electric power industries, machine-building industry – in all industries where waste gases with the temperature from 150°C to 1000°C are used in production.
Heat recovery in WHRS allows saving up to 30-40% of the consumed energy. Apart from the economic effect obtained from WHRS implementation, there is also a significant ecological effect due to lower heat emissions into the atmosphere as a result of considerably reduced waste gas temperatures in WHRS. So, the use of heat-exchanging units developed by Kalugin JSC allows reducing costs for consumption of energy resources (coke, gas, etc.), reducing production costs, increasing a company’s profitability and competitiveness.
For 17 years of operation at the market of heat-exchanging equipment Kalugin JSC implemented over 50 projects for WHRS construction at plants in Russia, Kazakhstan, Ukraine, Turkey, Syria, India and China. The average payback period after WHRS commissioning is six months to three years, the service life is minimum 10 years.
When developing a WHRS design, we analyze operating parameters of existing thermal plants and study structural features of the production site where erection of the new system is planned. Having received required data, we make calculations which can be used as a basis by the customer to choose a WHRS design with the most efficient operating parameters of heat-exchanging units which would satisfy the highest requirements for economic efficiency and payback period.
At present our most efficient heat-exchangers are heat pipe heat-exchangers (Fig.1) and plate heat-exchangers (Fig.2).
Fig. 1 Heat Pipe Heat-Exchanger
1.Separation Wall. 2. Shell. 3. Heat Pipes
Heat pipes of this type can be used in heat-exchangers of “gas-gas”, “gas-liquid”, “liquid-liquid” and “liquid-gas” types.
Even damage of several heat pipes doesn’t lead to failure of the entire heat-exchanger. Failed heat pipes can be replaced at any planned shutdown of the process plant. Unlike tubes used in recuperators, moisture from heat carriers doesn’t condense on heat pipes. It helps avoid intensive corrosion of heat pipes and dust sticking to their surface and results in longer service life of heat pipe heat-exchangers in comparison with tube recuperators.
Due to helical finning, they have a considerably larger heat-transfer area. They have a space-saving design, they are less metal-consuming, they can be installed at small production sites and they are completely safe and reliable in operation. Moreover, as compared to tube recuperators, they have a lower cost of manufacturing. Designing, manufacturing and commissioning of this heat-exchanger takes about 8 to 10 months with the guaranteed service life up to 10 years. The payback period for equipment of this type is 6 to 18 months
Fig.2 Plate with finning made by laser welding
Due to special features of laser welding, welds on the plate are not different from the base metal. These welds are full-strength, plastic, allowing bends and local deformation, not corrodible (including intercrystalline corrosion).
The developed technology makes it possible to manufacture plates of corrosion-resistant (including heat resistant) steels and alloys with the service temperature up to 1100-1250°C. It is also possible to make bimetallic weld joints (for example, the plate is made of one steel or alloy and the fins are made of another steel or alloy) and produce heat-exchangers made of heat-resistant metal on the high-temperature side and common stainless or low-carbon steel on the low-temperature side. This can be quite useful considering high prices for stainless and, particularly, heat-resistant steels.
Combining finned plates in this way, we build up new blocks of heat-exchangers. Their design is very simple (Fig.3) and represents “a layer cake” made as alternating cavities filled with heating and heated fluids. To provide the desired capacity of the heat-exchanger, it is necessary to assemble the required quantity of plates in a block and choose a heat-exchanger arrangement (Fig.4). At the inlet and outlet of the gas lines, diffusers and confusers are installed. Between the heating blocks, at the inlet and outlet of the heating and heated lines, temperature expansion joints are installed.
Fig.3 Heating Block of Heat-Exchanger Fig. 4 Plate Heat-Exchanger
Different combinations for positions of plates and heating blocks relative to each other make it possible to create single-pass and multipass heat-exchangers.
The block design facilitates erection, maintenance and repair of heat-exchangers. Open access to the channels of gas lines provides examination and cleaning of channels and relatively small aerodynamic resistance allows high velocities of gas flows (more than 14 m/s), which helps avoid dust buildup in the channels deteriorating parameters of heat-exchangers.
Research has shown that due to small thickness of the parts the new heat-exchangers have additional advantages: fast response, high thermal plasticity, which is especially important at unsteady temperatures of waste gases, for example, waste gases from shaft furnaces and cupola furnaces with a wide range of working temperatures (200-1000°) within a small period of time.
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