Recuperative Burners Research Articles

Deep-learning-based reduced-order modeling to optimize recuperative burner operating conditions

This study analyzed a recuperative burner system that is critical for energy efficiency and pollutant reduction in the firing processes required in the manufacturing industries. We aimed to optimize the operating conditions of a recuperative burner using computational fluid dynamics (CFD) combined with a novel reduced-order deep-learning technique. The Reynolds-averaged Navier–Stokes model and finite-rate/eddy-dissipation models were used to generate reliable CFD simulation results considering four operating conditions (temperature and mass flow rate of air and fuel). We first validated the CFD model with two-dimensional axis-symmetric experimental burner results and created a proper orthogonal decomposition transformer model using large-scale snapshots of the CFD results and various operating conditions. Subsequently, a genetic algorithm was employed to find the optimal conditions for five different objective functions: fuel economy, decrease in carbon monoxide emissions, reduction in nitrogen oxide emissions, decrease in carbon dioxide production, and an all-encompassing view of the four objectives. Finally, by comparing our proposed approach with previous methods, we confirmed that the obtained optimal operating conditions improve the performance of the recuperative burner. This study provides an optimized framework for recuperative burners to reduce environmental pollution, with potential applications in many industries, such as ceramics, steel, and batteries.

EXPERIMENTAL RESULTS ON THE IMPLEMENTATION AND USE OF RECOVERY BURNERS

The article presents the main aspects of the implementation, use and pilot and industrial experiments of some self-contained recovery burners. The results of pilot and industrial experiments of these burners have argued and quantified their energy efficiency. This efficiency consists mainly in an economy of specific fuel consumption (natural gas and / or coke gas) of approx. 25-35%. Other advantages of using recuperative burners are: ensuring a higher temperature in the hearth, reducing the duration of the processing cycle and thus increasing labor productivity. All these advantages of using recuperative burners are based on their operating principle, which consists in preheating the oxidizer (combustion air) by recovering an important part of the enthalpy of its own flue gases. This recovery is done in an energy recuperator designed right in the body of the recuperative burner. Due to this important aspect, the recovery burner is part of the Primary Energy Recovery (REP) category.

ASPECTS REGARDING THE CONCEPTION, DESIGN AND CONSTRUCTION OF RECUPERATIVE BURNERS

This article presents the main aspects of the conception, design and construction of self-designed recuperative burners. The starting point of the article is the operating principle of this specific type of combustion plant. This operating principle is based on the preheating of the combustor (combustion air) by taking over an important part of the enthalpy of its own combustion gases. Based on this principle, the recuperative burner of our own design has an energy efficiency that consists in reducing the specific consumption of fuel (natural gas) by about 25-35%. Also, the use of this specific type of combustion plant provides other functional advantages such as: a higher temperature in the hearth (due to a complete combustion), reduction of technological cycle times for the realization of various processes. The article also presents some functional parameters of a type-dimensional range of recuperative burners of our own design.

Methodologies of heat calculation and selection of rational parameters of regenerative burners operation

Decrease of energy intensity of products is an actual task for all the industries, including steel industry. One of the best solutions to increase energy efficiency of heating facilities is application of recuperative and regenerative burners, which ensure high temperature of air heating. Such high temperatures cannot be achieved at application of heating systems based on central recuperator. It was shown that many countries accomplish studies to perfect recuperative burners and simulation of their thermal operation. However at present there are no universally recognized methodologies of calculation and designing of such equipment. Results of studies presented, which were implemented in three methodologies intended for heat calculation and selection of rational parameters of regenerative burners operation. The methodologies enable also to determine a fuel utilization coefficient for a furnace system based on regenerative burners, to estimate competitiveness of solutions at creation new and modernization existing furnaces comparing with utilization of modern central recuperators. Comparative simplicity of the mathematical apparatus used in the methodologies highlighted, as well as correspondence of the used calculated expressions to the physical nature of the processes taking place. Besides, the methodologies enable during calculation to set the values of important characteristics, which can be reached based on determination of values of basic structure parameters of lining. A scheme of joint application of the elaborated methodologies proposed.

Assessment of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces

The present study investigates the application of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces and their economic potential for decreasing carbon dioxide emissions in this field of application. Doing so, a detailed technological analysis of several influencing parameters on the heating system was performed as well as a consideration of furnace heating technology challenges. Starting with an evaluation of the main thermophysical properties of the blends and their corresponding flue gases, requirements for the heating systems were identified. Potential ways of decreasing flue gas losses and increasing the heat transfer are shown. In the radiant tube application, an increased overall combustion efficiency of about 1.2% was measured at 40 vol% hydrogen in the fuel gas. Influences on the air to gas ratio control system of the furnace is a further important point, which was considered in this study. Two commonly used control systems were evaluated concerning their capabilities to regulate the gas flow rates of blends with varying hydrogen contents and combustion properties, such as Wobbe Index. This is important, since it shows the capability to retrofit existing furnaces. Two types of burners were tested with different natural gas/hydrogen blends. This includes an open jet burner with air-staged and flameless combustion operation modes. A recuperative burner for radiant tube application was considered as well in these tests. Doing so, the nitrogen oxide formation of both systems under different operating conditions and different fuel blends were evaluated. An increase by about 10% at air-staged combustion and about 100% at flameless combustion was measured by a hydrogen content of 40 vol% in comparison to pure natural gas firing. Finally, the additional fuel costs of natural gas hydrogen blends and different cases are presented in an economic analysis. The driving force for the use of hydrogen as a fuel is the price of the CO2 certificates, which are considered in the analysis at a current price of 25.2 €/t CO2.

Optimization of the built-in recuperator surface of recuperative burner according to the criterion of energy coefficient maximum

The recuperative burners is a modern direction of reducing fuel consumption during the heat treatment of metals in furnaces. Their use can significantly reduce fuel consumption. Despite the evident advantages, the spread of such equipment is constrained due to its high cost. The research is conducted for determining ribs rational profile and optimizing mass and size characteristics of a built-in recuperator. There are results that make it possible to reduce either the recuperator mass or its aerodynamic resistance. However, such changes contradict each other, so a compromise solution must be found. Currently, there are no generally accepted methods of thermotechnical calculations for recuperative burners. This work aims to develop a methodology to optimize the built-in recuperator surface according to the criterion of maximizing the energy coefficient. To conduct the study, the elements of recuperative heat exchange theory for counter-flow media were used. The proven methodology for determining the temperature of heated air and cooled combustion products after recuperator was applied. Also, the known concept of energy coefficient was used for the research. A technique has been developed to optimize the surface of the incorporated heat exchanger according to the criterion of maximizing the energy coefficient. The technique includes composing an expression for determining the energy coefficient, taking its derivative and equating it to zero with further solving the obtained equation with respect to heat exchange surface. The developed method was used in the recuperative burner with the thermal power of 500 kW. For the range of heat transfer coefficient 75–200 W/(m2·K) associated to the smoothtube part, a fifth-degree polynomial has been determined which describes the dependence of the smoothtube part optimal value of a built-in recuperator surface on the heat transfer coefficient. The developed technique is important for recuperative burners design, for increasing their efficiency and reducing their production cost. The methodology error associated with the assumption that the heat transfer coefficient is constant when the length of the built-in recuperator changes does not exceed 5 %.

Analysis of modern trends in recuperative burners perfection

At present, recuperative burners are becoming more extended in the gas-heated facilities, thanks to their significant advantages comparing with conventional gas-burning devices. However, the wide application of the recuperative burners is restricted by their high price. Therefore, studies for perfection recuperative burner designs and technologies of aggregates heating with the burners application are very actual. Results of analysis of modern ways of the burners designs and methods of their application presented, including diagnostics of the recuperative burner heat-exchanging surface state, optimization of the heat-exchanging surface and others. Items of ribbing rational parameters selection for imbedded recuperative devices considered. Perfection of the preliminary combustion chambers and air distribution by combustion stages are important ways of the recuperative burner perfection. It was noted, that in addition to traditional two-stage combustion systems, three-stage combustion systems are appeared lately. It was showed, that under unfavorable conditions of a furnace running, a significant contamination of the recuperative device surface can take place earlier comparing with the set regulation time of periodical cleaning, resulting in losses related to increase of fuel consumption. From the other side, unjustified decrease of the furnace operation period between the recuperative device surfaces cleaning is inconvenient in organization. A methodology of operative diagnostic of a recuperative device state elaborated, due to which the estimation of the imbedded recuperative device heat-exchanging surface state can be done by the identification of the current values of recuperation coefficient and their comparing with the standard values. The methodology enables regulating the periods of cleaning of the surfaces of both the central recuperative devices and recuperative burners.

Function Value-Based Multi-Objective Optimisation of Reheating Furnace Operations Using Hooke-Jeeves Algorithm

Improved thermal efficiency in energy-intensive metal-reheating furnaces has attracted much attention recently in efforts to reduce both fuel consumption, and CO2 emissions. Thermal efficiency of these furnaces has improved in recent years (through the installation of regenerative or recuperative burners), and improved refractory insulation. However, further improvements can still be achieved through setting up reference values for the optimal set-point temperatures of the furnaces. Having a reasonable expression of objective function is of particular importance in such optimisation. This paper presents a function value-based multi-objective optimisation where the objective functions, which address such concerns as discharge temperature, temperature uniformity, and specific fuel consumption, are dependent on each other. Hooke-Jeeves direct search algorithm (HJDSA) was used to minimise the objective functions under a series of production rates. The optimised set-point temperatures were further used to construct an artificial neural network (ANN) of set-point temperature in each control zone. The constructed artificial neural networks have the potential to be incorporated into a more advanced control solution to update the set-point temperatures when the reheating furnace encounters a production rate change. The results suggest that the optimised set-point temperatures can highly improve heating accuracy, which is less than 1 °C from the desired discharge temperature.

Study of Thermal Performance of Modern Design of the Drum-type Batch Furnace

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THE USE OF ENERGY EFFICIENT TECHNOLOGIES IN THE FRAMEWORK OF IMPLEMENTATION OF INVESTMENT PROJECT «ORGANIZATION OF PRODUCTION OF ROLLED BAR IRON WITH THE CONSTRUCTION OF SMALL-SECTION WIRE ROLLING MILL» OJSC «BSW – MANAGEMENT COMPANY OF HOLDING «BMC»

This article reveals the main energy efficient solutions and innovations implemented in the framework of the investment project «Organization of production of rolled bar iron with the construction of small-section wire rolling mill» in the open joint stock company «Belarusian metallurgical works (BSW) – Management Company of Holding «Belarusian Metallurgical Company (BMC)». This project was included in the list of the most important projects for the creation of new enterprises and industries that are crucial for the innovative development of the Republic of Belarus. Supplier of technology and equipment for the project were made by the company Danieli & C. Officcine Meccaniche SpA (Italy). The modern and unique equipment used in this investment project allows to use more than 90% of fuel and energy resources (by using the heat recuperator of flue gases, heat recovery boiler, recuperative burners, etc.). Implementation of the project allowed to carry out the maximum processing of production and to receive new production with higher added value.

EXPERIENCE IN USE OF RECUPERATIVE BURNERS DEVICES IN FURNACES OF PERIODIC ACTION FOR HEAT TREATMENT OF BLANKS IN SPC-2 OJSC «BSW – MANAGEMENT COMPANY OF HOLDING «BMC»

In building and modernizing industrial furnaces the following important factors should be taken into account: on the one hand, economic efficiency must be ensured, and on the other hand it is important to reduce harmful emissions into the atmosphere, improve the working conditions of personnel, etc. At the same time, constantly increasing requirements for productivity and environmental friendliness should not adversely affect the period of cost recovery.This article considers the experience of using recuperative burners. Both positive and negative aspects of the use of burners are considered from the point of view of economics, ecology and technology.An important initial point of cost optimization is the correct choice of a heating system complete with an automatic control system. One example of an effective heating system is a burner with a built in air heating system (recuperative burner), which saves fuel, reduces harmful emissions and simultaneously improves the technical and economic performance of the furnaces.

Combustion peculiarities of coal-methane-air mixtures in a recuperative burner

Numerical modeling of the combustion of a lean methane-air mixture containing fine coal particles entering the “Swiss-roll” type recuperative burner is considered. The mathematical model is constructed under the following assumptions: the flow field is two-dimensional; the gas mixture is an ideal incompressible gas consisting of oxygen, methane, coal volatile substances, carbon monoxide, carbon dioxide, water vapor, hydrogen and nitrogen. In the gas phase four oxidation reactions, in which methane, volatile matter of coal, carbon monoxide, hydrogen participate and the reaction of carbon dioxide decomposition take place. On the surface of the coal particle, there are three oxidation reactions involving oxygen, carbon dioxide and water vapor, resulting in the formation of carbon monoxide. It is assumed that coal contains 8% of ash, 12.9% of volatile substances and 79.1% of carbon. It is shown that for a two percent methane-air mixture the reaction zone shifts toward the center of the burner as the feed rate of the mixture increases. An increase in the content of coal particles leads to a shift of the reaction zone into the inlet part of the burner, and the heat release in the burner increases.

Методика прогнозирования теплотехнической эффективности использования рекуперативных горелок

Методика прогнозирования теплотехнической эффективности использования рекуперативных горелок

Burning stability of the coal-dust methane-air mixture in a recuperative burner

The physical mathematical model of combustion of the coal-dust methane-air mixture in a recuperative burner has been developed. The influence of the particles (inert and reacting) on the burning stability of coal-dust methane-air mixture with low concentration of methane has been determined. The regimes of stable combustion for lean methane-air mixture with coal suspension depending on the fuel flow rate at the inlet of the burner and the fuel content have been defined.

Numerical investigation on burning stability of the coal-dust methane-air mixture in a recuperative burner

The paper is devoted to numerical investigation on combustion singularities of the bi-dispersed coal-dust methane-air mixture in a slot recuperative burner. The aim of the research is to determine the stable combustion conditions of the methane-air mixture depending on the fuel flow rate at the inlet of the burner and on the parameters of the mixture (the particle size and the mass concentration of the coal particles, the percentage composition of inert particles and the methane volume content). The problem was solved by finite difference method. The regimes of stable combustion for the coal-dust methane-air mixture depending on the fuel content and the fuel flow rate at the inlet of the burner the have been defined.

Low scale reheating of semi-finished metal products in furnaces with recuperative burners

Industrial furnaces for reheating semi-finished metal products are often direct fired with natural gas and air. Oxidation of the metals exposed to the furnace atmosphere causes significant material losses and additional work during furnace operation and in further processing. A reheating concept, which reduces scale formation, was developed for direct fired reheating furnaces. It involves fuel rich combustion, post-combustion of the unburned off-gas and efficient preheating of the combustion air. This paper focuses on the reheating of copper and steel in direct fired furnaces with recuperative burners. Therefore, the post-combustion in an annular gap, according to a recuperative burner was examined, concerning temperature profile in the gap and off-gas emissions, to determine technical limits of the concept. Based on energy balances and scale formation the costs for fuel and metal loss were calculated to determine economic impact on the reheating process. The results show economic potential of the concept in terms of cost savings for the reheating of copper with a fuel rich combustion but no significant cost savings for the reheating of steel.

Numerical investigation on post-combustion in a burner for heat treatment furnaces with a reducing gas atmosphere

Scale formation in reheating and heat treatment furnaces causes a significant metal loss on semi-finished metal products. The presented project is about the development of a burner that produces a low oxidizing / reducing atmosphere in the furnace with a thermal efficiency comparable to state-of-the-art recuperative burners. The concept combines direct fuel rich firing and indirect heating with radiant tubes in a recuperative burner. Unlike existing recuperative burners, the concept-burner is equipped with an open radiant tube (ORT) forming an annular gap between the burner and the tube, where the off-gas is post-combusted by the addition of secondary air. The heat of reaction is either transferred to the furnace by radiation of the ORT or recuperated to heat up the primary and secondary combustion air. In the presented numerical study, the impact of the primary equivalence ratio, the furnace temperature and the total equivalence ratio ϕtotal on the post-combustion process in the annular gap is evaluated. The total equivalence ratio has the most significant influence on post-combustion. The results for the variation of the total equivalence ratio ϕtotal show a faster post-combustion can be reached by using a lower total equivalence ratio of ϕtotal = 0.87 instead of ϕtotal = 0.91. Another parameter on post-combustion is the primary equivalence ratio ϕprimary. At ϕprimary = 1.43 the amount of H2 and CO in the primary off-gas is higher, resulting in a slower post-combustion. At the same time the combustion at ϕprimary = 1.11 is delayed because of lower mixing rates and kinetics. A variation of the primary off-gas inlet temperature has a low impact on the post-combustion. Decreasing temperature from 1050 °C to 950 °C delays the reaction. The results show that there is a good correlation between the calculations and the measurements at the experimental setup. Therefore, the numerical model is capable to show the impacts of the different parameters on the post-combustion.

Development of an Energy-Efficient Burner for Heat Treatment Furnaces with a Reducing Gas Atmosphere*

Abstract One of the main reasons for metal loss of semi-finished metal products during heating in reheating and heat treatment furnaces is scale formation. In the presented project a burner is developed which produces a low oxidizing / reducing atmosphere in the furnace. The concept is realized by a recuperative burner, which generates a reducing furnace atmosphere due to fuel rich combustion of natural gas and air. The complete combustion of the furnace atmosphere is ensured by the injection of additional air and takes places in an open radiant tube resulting in a high energy efficiency. In this paper numerical and experimental results are presented and discussed. The numerical results showed the huge impact of the secondary air swirl on the post-combustion in the annular gap which is formed between the open radiant tube and the burner. Mixing phenomena in the annular gap results in a nearly complete post-combustion at low and high swirl angles of the additional combustion air (ω = 0°, ω = 90°). Instead of that, at a swirl angle of ω = 45° the entire reaction from CO to CO2 was not ensured within the boundaries of the numerical model. The quality of the post-combustion was experimentally evaluated by measuring the CO-emissions in the off-gas channel. These were lower than 50 mg/m3 in a wide range of operation. The NOx-emissions are lower than 121 mg/m3 at all tested cases.

Investigation of the Combustion Stability of Methane-Air Mixture in Recuperative Burners of Different Geometries

The results of numerical investigations of 5.5% methane-air combustion stability in heat recuperative burners (counter flow burner, U-shape burner and Swiss-roll burner) are presented in this paper. The investigation is carried out with the use of commercial CFD package Ansys-Fluent. The boundaries of combustion stability of 5.5% methane-air mixture depending on the gas flow rate at the inlet of the burners are determined.

COMPLICATED EXTERNAL HEAT EXCHANGE IN THE VERTICAL CHAMBER FURNACE DESIGNED FOR HEAT TREATMENT OF LONG PRODUCTS

Calculation of the external heat exchange in the combustion furnaces is always complicated because of insufficient knowledge of the convective heat transfer characteristics. It is extremely important to know the above-mentioned characteristics as the modern hating furnaces are equipped with the high-speed burners providing for running of the gas-air mixture at a speed of 100 – 150 m/sec. The present article demonstrates a procedure and results of the investigation of the complicated external heat transfer in the operating industrial furnace equipped with high-speed recuperative burners and lined with ceramic-and-fibrous blocks. The article also includes the recommendations on application of the submitted procedure and results of the abovementioned investigations.