At the end of 2013 KALUGIN’s experts implemented an innovative turnkey project of the waste heat recover system (WHRS) of the blast furnace by preheating the combustion air in the plate heat-exchanger and supplying it to tuyeres of the blast furnace no.4 at OAO Ufaleynickel
(Verkhny Ufaley, Chelyabinsk oblast).
Commissioning of the system, including preparation of the detailed documentation of WHRS and the heat-exchanger, manufacturing, supervision, start-up, and adjustment works were performed only for three months from the date of contract conclusion.
The implemented waste heat recovery system has a high coefficient of thermal efficiency, low aerodynamic resistance in air and flue ducts, high heat resistance (operating temperature of the heat-exchanger is 300-600 C). Application of the plate heat-exchanger showed that it is possible to use WHRS with flue gases which have high concentration of dust. The result of the use of WHRS with the plate heat-exchanger during the first months was substantial energy saving. For example, due to combustion air pre-heating the coke rate per each smelting of crude ore was reduced, flue gas emission was reduced, the heating load on the environment was decreased. Considering low energy efficiency of iron and steel works at many Russian enterprises, it should be noted that implementation of such equipment acquires special importance.
We are talking with General Director of KALUGIN JSC M.Kalugina about experience in WHRS implementation in iron and steel production.
160 Kalugin shaftless stove systems are used in Russia, China, India, Ukraine, Japan, Kazakhstan, Syria, Indonesia. Hot blast stoves in Turkey and Brazil are getting ready for commissioning.
Dear Ms.Kalugina, please tell us about your company’s experience in implementing the waste hear recovery system in iron and steel production.
As you know, KALUGIN JSC specializes in development of high-temperature shaftless hot stoves for blast furnaces, and various systems of waste heat recovery. We started to develop waste heat recovery systems in the early 2000s, when metallurgists started to introduce into production Kalugin shaftless stoves (KSS) developed by our company. KSS allows increasing the hot blast temperature in blast furnaces up to 1300-1400C, and this, in its turn, required increase of the stove dome temperature which means additional use of natural gas. However, in a number of countries, such as China, natural gas in metallurgy was not almost applied, for that reason searching for alternative energy source was long overdue. To solve this problem we developed different heat recovery systems which provided preheating of combustion air and blast-furnace gas up to 150-180C in heat-exchangers while using heat of low temperature waste gases from hot stoves with the temperature of not over 300C. Thermosiphon heat-exchangers proved to be the most effective. They are less metal-consuming, absolutely safe, and reliable in operation; their price is much lower than the tube recuperator’s. Development, manufacturing and commissioning takes 8-10 months and the guaranteed service life is ten years. Pay-back period is 1-3 years. Currently, over 40 heat recovery systems with thermosiphon heat-exchangers are installed at different stove systems: 38 systems at iron and steel works in China, two systems in Russia (blast furnace no.4 at Severstal Iron and Steel Works and blast furnace no.7 at Novolipetsk Iron and Steel Works). In addition, eight tube heat-exchangers were built by our company in India and Ukraine. Therefore, implementation of different heat recovery systems, especially in blast-furnace practice, is high in demand and an effective option allowing metallurgists to smelt metal without additional use of natural gas to heat hot blast which significantly reduces net cost of iron smelting. Their operation does not require operating personnel and extra expenses. Moreover, such systems can be effectively used in heat- and electric-power industry, machine building, in manufacturing construction materials, in chemical and petrochemical industry — everywhere where there are low temperature waste gases with the temperature up to 300C.
In 2013 we received a proposal from Ufaleynickel to develop a waste heat recovery system for blast furnace no.4 of old late 1930s design. Considering waste gas temperature (200-600C, maximum 900C), high dust content (5.5—40 g/m3), high amount of impurities and corrosive agents, lack of optimal possibilities to arrange and erect a heat-exchanger, we together with Ufaleynickel chose a plate heat-exchanger made of finned thin-walled panels which became the main element of waste heat recovery system.
Technical specification of the plate heat-exchanger:
• waste gas temperature — 300-600 C, maximum 900C;
• waste gas volume — 170,000 Nm3/hour;
• waste gas dust content — 5.5-40 g/Nm3;
• heated air volume — 65,000 Nm3/g;
• air temperature before preheater— 20C;
• air temperature after pre-heater — 300C;
• dimension — 5.7х7.9х3.9 m, weight 30.6 t.
How difficult was the project?
To implement the project, KALUGIN’s experts calculated the whole thermal scheme of the system, its dimensions and mass, developed project documentation, datasheet and operation manual according to scientific heat engineering methods. Everything was taken into account: how it would look like, what height the fins should have been and distance between the fins, length and width of plates for waste gases and air, what kind of pipes, fitting, throttles, valves, gates would ensure claimed specification.
A number of interesting technical solutions for implementing the object on operating furnaces were found in the course of design work. Waste gases are removed from a blast furnace by four lined collectors which automatically imply installation of four heat-exchangers and require serious and expensive reconstruction of the whole smoke removal system.
We suggested using one heat-exchanger on the existing chimney stack. Therefore, on this stage of the project a lower price of construction of the system was provided to a customer, the cost of instrumentation and automation was reduced by several times and the more convenient operation was applied.
How complicated these projects are in the production?
To implement the project, we had to solve three main tasks: first, to fit in the very tight deadlines of WHRS implementation (the project should have been done for three months during the scheduled reconstruction of the blast furnace proper), secondly, to have time to manufacture it within the time limits, thirdly, to assemble under conditions of operating plant, limited space and with existing steel structures. It is important to note that in the plate heat-exchanger of KALUGIN design over 600 finned plates manufactured according to the unique technology of laser cutting and welding gathered for three heating units with 200 panels each. The weight of each unit is more than 9 t. To my knowledge, in Russia only 2-3 companies can manufacture finned panels of required quality. One of the companies is located in Ekaterinburg. So that, all the panels were manufactured on the equipment unique for our country. For this purpose we developed and manufactured special fitting. Moreover, each ready panel was inspected for welding quality at the special stand developed by KALUGIN. Due to big dimension and weight, the heat-exchanger was manufactured and assembled on site. But all the tasks were successfully completed and WHRS was put into operation at the same time as the blast furnace was blown-in after capital repair.
Did you apply new engineering solutions while developing heat-exchanger’s plates?
Yes, we did. At present we applied for the patent.
Why did you use a plate heat-exchanger and not a conventional one?
First of all, we have been working in accordance with the design assignment given by the customer. In his opinion, such type of WHRS most closely corresponds to the production process. At the stage of discussion and contract conclusion we suggested implementing a proven thermosiphon heat-exchanger. But the pay period of this type of the heat-exchanger is longer as compared with the plate heat-exchanger’s and there was not enough space for its installation. Besides, plate heat-exchangers unlike thermosiphon heat-exchangers can operate at higher temperatures and this, probably, determined the choice. We made appropriate recommendations to the customer. It is important that in dusty condition when the operating temperature goes down below 300C, dust can stick to the plate walls which in future can influence operation of the whole system. At this moment high cold air intake occurs, the combustion process goes less intensive, the waste gas temperature reduces to 200C and lower. To avoid a negative scenario, a blast furnace is necessary to shut down for timely maintenance or to take additional measures to preheat waste gases to the required temperature and to maintain it.
Do you have data of heat-exchanger’s economic efficiency in steelmaking industry?
I know that our latest development allowed Ufaleynickel to bring back 20% of heat without additional source of energy and, thus, to reduce the rate of expensive coke. Consequently, only due to coke saving it is possible to repay expenses for 6-8 months and to work with profit. On a year-over-year basis, benefit of implementation of such heat recovery systems can be tens millions rubles.