Boiler Design Research Articles

Performance and Flexibility Improvements of Staged Pressurized Oxy-Combustion

Staged Pressurized Oxy-Combustion (SPOC) is a low-carbon coal combustion power technology being developed by Washington University in St. Louis (WUSTL). Oxy-combustion plants enable straightforward capture of carbon dioxide (CO2) by removing most of the nitrogen in the combustion air prior to use, thereby burning fuel in near-pure oxygen instead of air, producing a flue gas containing primarily CO2 and water. CO2 capture at amounts > 90% is possible, often using cryogenic air separation. Oxy-combustion typically relies on flue gas recycle (FGR) to reduce the peak temperature and radiation that would otherwise occur in a fuel/oxygen only flame. SPOC reduces the peak temperatures of combustion by utilizing two or more pressurized boiler modules connected in series to produce fuel staging; hence, only a portion of the fuel is combusted in any given furnace module. This means that the thermal energy released at each stage can be captured and removed from the gases prior to subsequent stages, when more fuel is introduced. This allows the SPOC process to operate with minimal FGR, avoiding the associated efficiency losses and additional costs. Also, the process operates at an elevated gas-side pressure, reducing boiler size, enhancing heat transfer to achieve a compact boiler configuration as compared to an atmospheric-pressure boiler design, and allowing for recovery of the latent heat of the water from the flue gas at a temperature useful to the steam cycle. The resultant net efficiency of the system is over 3 percentage points greater than traditional atmospheric-pressure oxy-combustion, and 7 percentage points greater than the post combustion variant, representing a step-change improvement over first-generation capture technologies. To further develop the concept, WUSTL and the Electric Power Research Institute, Inc., organized a project with American Air Liquide, Inc., Doosan Babcock Limited, and the U.S. Department of Energy to investigate a practicable and workable boiler design. The team has identified the potential for enhanced process flexibility for controlling power generation over a wider load range than is normally available to conventional coal-fired power plants due to the staged nature of the heat release. With increasing intermittent renewable generator contribution, on-demand generators need to be highly flexible to participate in the future energy market, requiring extensive operation at reduced load. Conventional coal-fired steam generators typically face challenges in maintaining temperature control of the reheat steam and main steam at reduced loads. This results in inefficient operation, both in terms of the boiler efficiency and steam turbine heat rate. The results of this project show the SPOC process is capable of exceptional turndown, both on a stage basis and with the ability to bypass entire stages. Oxygen-supply flexibility was also investigated, as this is also a key consideration for the overall flexibility of the SPOC process given the operating constraints of conventional air separation units. A boiler design concept assessment was conducted and was focused on delivering compact and constructible design. The assessment checked appropriate tube operating metal temperatures at full load and at lower operating loads, balanced against the needs of efficient coal combustion, and the resultant slagging and ash environments. Combustion testing in the 100-kWth pressurized combustion test rig at WUSTL was carried out to validate the combustion, heat flux profiles and burnout at multiple loads. Combustion parameters investigated were flame stability, fuel burnout, ash composition, radiative heat flux, and temperature profiles. The results of these tests formed the basis of a full-scale boiler design that will encompass improvements in both efficiency and flexibility over conventional oxy-combustion processes. The air separation unit flexibility was investigated, and associated cost implications were addressed. Detailed economic assessment results for a 550 MWe net power block are also provided, allowing for a comparison against the baseline NETL oxy-combustion and post combustion capture cases.

Coupled heat transfer model for the combustion and steam characteristics of coal-fired boilers

This paper presents a coupled heat transfer model for coal-fired boilers that integrates boiler’s fire side computational fluid dynamics (CFD) solution with the boiler’s steam cycle, and thus, can predict the boiler steam temperatures subject to different boiler design and operation conditions. In this coupled model, the heat transfer submodels describing the gas-steam heat exchange for each part of boiler heating surfaces are integrated by exchanging the steam temperatures iteratively. This coupled heat transfer model is self-consistent since it ensures the fire side heat transfer solution to always coincide with the steam temperature changes across each boiler heating surface. This model is specifically designed to provide efficient computational solutions to engineering boiler problems in which the changes of boiler steam temperatures subject to different boiler design and operation conditions are of the major concerns. This model is applied to a 320 MW subcritical boiler to evaluate the impacts of coal switching and boiler operation adjustment on boiler’s heat transfer distributions and steam temperatures. The simulation results demonstrate that this model can effectively capture the complex coupled heat transfer behavior between the fire and steam sides of boiler and serve as an efficient predictive tool for engineering boiler problems.

Design of vertical fire tube boiler using IBR code and FEA analysis

Design of vertical fire tube boiler using IBR code and FEA analysis

Combined scheme of solid fuel combustion in low power boilers

Different constructive schemes of solid fuel combustion in heating boilers up to 100 kW with the analysis of their efficiency depending on the quality of the burned solid fuel are considered. It is established that low-power solid fuel boilers with various types of combustion devices depending on the characteristics of the burned fuel and the accepted level of service are used in heat supply systems of premises, buildings and structures: from simple furnaces with manual maintenance to automated combustion devices of complex design. Mostly pre-prepared high-quality fuel is used for combustion: fuel pellets, briquettes, high-quality coal, the high cost of which significantly increases operating costs. In order to reduce capital and operating costs, it is advisable to introduce relatively inexpensive models of low-power heating boilers with an acceptable level of mechanization of combustion technology of cheap fuel, including local, with minimal costs for its preparation. The design of a heating water boiler with a semi-mechanical furnace and a technological scheme of combustion is proposed, which combines the processes of drying, gasification and combustion of fuel in a shaft with a clamping grate and combustion of coke in a layer on a moving grate. It is noted that the periodic supply of fuel in the furnace with a moving grate is maintained the stability of the combustion process in the combustion chamber, in the period between cleaning of ash and slag, without significant changes in the composition of above-layer gases. Due to the smooth movement of the next portion of hot coke from the fuel shaft to the combustion chamber on the rotating grate, conditions are created to maintain the uniformity of the boiler with the normative indicators. A reduction in harmful emissions in the exhaust gases was achieved during the combustion of the reaction fuel by passing a secondary blast of air through a collector and directing it to the combustion zone of light substances at the outlet of the clamping grate. Analytical equations for determining the size of the combustion zone according to the regime and design parameters of the combustion process are given. The efficiency of application of the combined (shaft-layer) technological scheme in low-power boilers was tested during testing of combustion of different quality coal in a semi-mechanical furnace with a rotating grate in the electric coal boiler with a heat output of 50 kW for railway carriages.

THE USE OF EXPERIENCE OF COAL COMBUSTION IN A CIRCULATING FLUIDIZED BED FOR DESIGNING OF MEDIUM CAPACITY STEAM BOILERS FOR BURNING OF WET WASTE OF COAL PREPARATION AND RDF IN UKRAINE

The necessity to implement advanced combustion technologies to utilize MSW/SRF/RDF and coal reject waste is an important problem for Ukraine to be solved. The introduction of such technologies will favor to involve annually about 2 mln t of RDF and partly cover deficit of bituminous coal, lack of which is currently faced. The technological niche for CFB combustion of RDF/SRF has certain optimal range bearing in mind technological, ecological (2010/75/EU Directive etc.) and financial performance. In view of this it seems reasonable to implement CFB for RDF/SRF firing starting from boiler steam capacity of 50-75 t/h while stoker firing of RDF could be efficiently implemented for lower range. The design of such boiler should rely upon lessons learned of commissioning and operating large-scale CFB boiler (having steam capacity of 670 t/h; 545/545 C) we obtained at Starobeshevo Power Plant in Ukraine. Accounting for the above the analysis of implementation and modifications made at large-scale CFB boiler (cyclones, seal pot, fluidized bed heat exchangers) has been done. The experience was used to design (along with KB “Energomashproekt”) medium-scale CFB boiler (having steam capacity of 75 t/h; 500 C) to burn high ash coal washering wastes and RDF/SRF. The sketch-3D-design of such boiler is presented with key performance. Bibl. 6, Fig. 4, Tab. 4.

Physical modeling of the M-shaped boiler furnace aerodynamics

In order to increase the thermodynamic efficiency of the Rankine cycle, in Russia, China, the USA, and EU countries, new-generation power units with advanced ultra-supercritical (A-USC) steam parameters are being developed. Using A-USC steam parameters (temperature – 700-760 °C, pressure – 35 MPa) will lead to the need to use expensive nickel steels. A single-shell design of the M-shaped boiler for burning Kuznetsk coal grade TP with solid slag removal (SSR) was proposed to reduce the total length of the main steam pipelines. A solid fuel combustion scheme with direct-flow burners, nozzles and system of vertical-horizontal tangential flames (VHTF) has been developed for this boiler, which will ensure: emissions of nitrogen oxides into the atmosphere at a level lower than standard; continuous operation of the boiler in the absence of slagging of the furnace walls and overheating of the pipe metal; a high degree of burnout of coal dust, with the provision of the standard value of the mechanical underburning of fuel; long minimum boiler load at a level not exceeding 40% of the nominal one according to the conditions of coal dust combustion stability.

Scale law of sCO2 coal fired power plants regarding system performance dependent on power capacities

Once supercritical carbon dioxide (sCO2) cycle is used for coal fired power plant with conventional boiler design (total flow mode TFM), ultra-large pressure drop of sCO2 boiler occurs to suppress system efficiency, thus we proposed partial flow mode (PFM). A CO2 stream is segmented into two parallel lines, each having half flow rate and half length. The effectiveness of PFM was examined at various power capacities (net power output Wnet) covering 50–1000 MWe. A numerical model is established by coupling thermodynamic cycle of system and thermal-hydraulic characteristics of boiler. Scale laws of boiler size, mass flux and pressure drop in boiler tubes are developed, agreeing with numerical simulation results. We show that with increase of Wnet, TFM increases pressure drops to generate additional pressure and load for compressors. This effect not only increases energy loads, but also raises exergy destructions for all components, deteriorating the first and second law efficiencies of the system. Compared with TFM, PFM reduces pressure drops according to the 1/8 criterion, the pressure drop penalty effect is eliminated to have much higher efficiencies than TFM. Because at smaller Wnet such as 100 MWe, sCO2 boiler has larger surface to volume ratio, flow passages of CO2 are sufficient to keep acceptable pressure drop, hence the system performance is similar when using TFM and PFM. We conclude that the flow splitting strategy is necessary for Wnet > 100 MWe, but not recommended only at very small power capacity such as Wnet < 100 MWe. Our work is important to understand the distinct feature of sCO2 cycle driven by different heat sources.

Categorization of small-scale biomass combustion appliances by characteristic numbers

The market offers a broad range of different combustion appliances dedicated to residential heating with biomass. The effect of fuel properties on the formation of slag and emissions varies and the technology influences the impact to a certain extent. The applicability of biomass fuels is not only determined by operational settings but also by the design of boiler components as grate area and combustion chamber. Aspects as the fuel load on the grate, residence time, geometry of grate and combustion chamber design, as well as feeding and de-ashing influence the extent of slag formation and emission release. The determination of characteristic numbers by means of constructional measures allows a systematic comparison and - in a further step - an assessment/categorization of combustion technologies. After conducting a boiler survey relevant parameters regarding grate, combustion chamber, feeding, and ash removal were gathered. Characteristic numbers were specified in order to compare technological aspects. The results of this study allow the investigation of the influence of the combustion technology on the performance. They will assist the systematic and targeted design of small-scale boilers and the optimization of combustion appliances in future, especially when it comes to fuel-flexibility.

Numerical study of oxy-fuel combustion behaviors in a 2MWe CFB boiler

Using modified IEA-CFBC(International Energy Association-Circulating fluidized bed combustion) model, a 2 MWe oxy-fuel CFBC boiler is simulated and analyzed as a promising solution to reduce greenhouse gas emission from coal power plants. This study evaluated and compared the oxy-combustion characteristics of various coals. Also, the effects of CO2 concentration (71–79 vol%), bed temperature (850°C) and coal properties on combustion efficiencies, CO2 concentration, acid gas emissions were analyzed. Because of their higher N2 and S content, sub-bituminous and bituminous coals were found to have SOx and NOx concentrations higher than those of anthracite. These simulation results from Oxy-fuel CFBC simulation of various coals can be used as operating parameters for design and development of commercial Oxy-fuel CFBC boilers.

Design and application of a novel coal-fired drum boiler using saline water in heavy oil recovery

In this paper, the design and operation of a novel coal-fired circulating fluidized bed (CFB) drum boiler that can generate superheated steam using saline water were introduced. The natural circulation water dynamics with a drum was adopted instead of the traditional once-through steam generator (OTSG) design, so that superheated steam can be generated for the better performance of the steam assisted gravity drainage (SAGD) technology in heavy oil recovery. The optimized staged evaporation method was proposed to further decrease the salinity of water in the clean water section of the boiler. The evaporating pipes of the salted water section were rearranged in the back pass of the boiler, where the heat load is low, to further improve the heat transfer safety. A CFB combustion technology was used for coal firing to achieve a uniform heat transfer condition with low heat flux. Pollutant control technologies were adopted to reduce pollutant emissions. Based on the field test, the recommended water standard for the coal-fired CFB drum boilers was determined. With the present technology, the treated recovery wastewater can be reused in steam-injection boilers to generate superheated steam. The engineering applications show that the boiler efficiency is higher than 90%, the blowdown rate is limited within 5.5%, and the superheat of steam can reach up to 30 K. Besides, the heavy oil recovery efficiency is significantly improved. Moreover, the pollutant emissions of SO2, NOx and dust are controlled within the ranges of 20–90 mg/(N·m3), 30–90 mg/(N·m3)and 2–10 mg/(N·m3) respectively.

The working status and deformation risk of membrane walls affected by the arrangement of burners in the arch-fired boiler

The thermal deformation of membrane walls is a severe safety issue in the arch-fired boilers, which is closely related to the combustion and flame inside the furnace. In this paper, various combustion schemes were conducted on a laboratory-scaled arch-fired boiler, exploring the correlations between the working status on membrane walls and the arrangement of burners. The influence mechanisms of the burners on the membrane walls were experimentally determined, with strong impact regions found on the front/rear wall in a relative wide of 0.6. The asymmetric combustion obtained in the furnace increased the temperature and strain/stress on the front wall with greater deformation risk, which should be avoided in the practical operation. The flameout of burners dramatically changed the local temperature and enhances the tearing risk of membrane walls with tension stress, which is consistent with the tearing track in the prototype boiler. Great correlations between the operation parameters (Tg, Tw, Tc, ε1 and σ1) and the and volumetric thermal load (Pv) were experimentally determined and considered applicable to the prototype boiler. While the impact range of burners helps estimating the uniformity of temperature and strain/stress on membrane walls, providing reference to the design and operation of similar boilers.

Analytical study vessel design of the portable patchouli oil steam boiler based on vacuum technology

Aceh geography is suitable for growing pogostemon cablin with high quality. Traditionally, patchouli oil extraction is carried out using distillation techniques. However, the results are unsatisfactory due to impurities substances presence in the boilers. High energy wastage is common in the traditional distillation technique process due to improper vessel design. The study aims to design and rate the vessel of portable distillate patchouli oil based on vacuum technology. The simplified vessel design and proposed vessel design were then tasted to find a proper design with respect to ASME boilers and pressure-related VIII Vessel Code. However, internal and external pressure employed in both design and operation, given that the simplified model is 56.91 MPa and Sa is 116 MPa. The vessel design is yield to proposed model stress (Kmean) ≤ Sa Kmea is 86.13 MPa and Sa is 116 MPa. The analytical calculation and simulation results show that von-mises stress is less than the allowable stress material.

Thermohydrodynamic analysis of the vertical gas wall and reheat gas wall in a 300 MW supercritical CO2 boiler

Supercritical CO2 (sCO2) Brayton cycle usually shows high efficiency and also has compact structure, which can be considered as a promising alternative in future coal-fired power plants. However, sCO2 boiler has different structures and configurations compared with the conventional steam boiler, especially for the arrangement of radiative heat transfer surfaces. Proper design of vertical gas wall and reheat gas wall is crucial to the success design of sCO2 boiler. In this study, a thermohydrodynamic model of radiative heat transfer surfaces was developed to predict pressure drops and wall temperature distributions. A sCO2 power cycle calculation model was employed to comprehensively analyze the influences of pressure drops on the thermal efficiency. A 300 MW sCO2 boiler was taken into account as the baseline case and thermohydrodynamic analyses of gas wall and reheat gas wall were carried out. The influences of flow directions and mass fluxes on wall temperature, pressure drops and thermal efficiency were obtained by the present models. Then, optimized structures of radiative heat transfer surfaces were proposed, i.e., vertical downward gas wall with tubes of φ34 × 4 mm and vertical upward reheat gas wall with tubes of φ57 × 6 mm. Accordingly, the net cycle efficiency achieved an optimized value of 50.07% under the conditions that the wall temperatures of radiative heat transfer surfaces did not exceed the allowable temperature.

The study of heart transfer during boiling process of organic fluid

The paper considers the problem of studying heat transfer inside the pipes of an evaporator of an organic Rankine cycle unit during boiling of an organic heat transfer fluid. Recently, the organic Rankine cycle units are increasingly used in various industries for the utilization of low-grade heat of various processing units. One of the main elements of these units is the evaporator in which vaporization takes place. The evaporator is a concurrent boiler. One of the problems in the design of concurrent boilers is the lack of knowledge of heat transfer during the process of boiling fluid. This paper presents a study of the heat transfer process inside a concurrent boiler. This study is carried out by creating a model of boiling organic fluid in the pipes of a concurrent boiler. The boiling model was implemented in the Ansys fluent software package. Using this model, the values of the heat transfer coefficient were obtained at each point of the evaporator pipe under consideration. After obtaining the values, the dependence of the heat transfer coefficient on the length of the pipe was analyzed. As a result of the analysis, it was determined that starting from the point of 0.6 m, the heat transfer coefficient sharply decreases by 3.5 times. The value of the heat transfer coefficient after the decrease section is at the level of 125 W/m2K over the entire length of the pipe. Thus, it was determined that under given initial conditions, with a pipe length of more than 1 m, heat transfer ceases to be effective.

Investigation into Factors Causing Damage to Low-Pressure Loop Evaporating Tubes of Large-Capacity Heat-Recovery Steam Generators

The article addresses factors causing damage—in particular, flow accelerated corrosion wear (FAC) of tube walls—to the evaporator operating in the low-pressure loop of the Ep-258/310/35-15.0/3.14/0.44-540/535/263 (P-132) heat-recovery steam generator used as part of a 795-MW combined-cycle plant. Factors influencing the FAC, namely, improper water chemistry, availability of gas shunts in the steam generator, and high mixture motion velocity in the tubes in combination with the flow path configuration, are described. The damages inflicted to the tubes and their locations in the heat-recovery steam generator low-pressure loop are described. It is shown that gas shunts in the heat-recovery steam generator result in an increased heat absorption and higher velocity of medium in the boundary tubes of low-pressure evaporator tube banks, which intensifies the tube’s wear process. It has been found that the water chemistry used for the Kirishi District Power Plant (DPP) heat-recovery steam generator was not the factor that caused damage to the low-pressure loop tubes. The Kirishi DPP steam generator was compared with other similar large-capacity heat-recovery steam generators. For analyzing the low-pressure evaporator performance indicators, the loop and the processes occurring in it were modeled using the Boiler Designer software. An analysis of the results from comparison of the steam generator design and performance characteristics has shown that it is necessary to change the two-phase mixture motion velocity in the Kirishi DPP steam generator low-pressure loop by modifying the design or operating parameters. The wear of the low-pressure evaporator tube walls was mathematically modeled, the results of which confirm that erosion wear is one of the main factors causing damage to the tubes. The erosion is caused by the intense dynamic effect of two-phase, high-velocity flow jets on the tube walls. General recommendations for decreasing the wear of heat-recovery steam generator tubes are given. It has been determined that the increased wear of tubes in the low-pressure loop of the P-132 steam generator at the Kirishi DPP is caused by a combination of a few factors, such as high velocity of steam–water mixture, availability of bends, and unsatisfactory quality of aligning the tubes at their welding places.

Aerodynamic Characteristics of a Stoker Furnace with Staged Combustion: Comparison of Cold Modeling Experiments and Numerical Simulations

A three-dimensional trial bed is established for a staged combustion boiler, and a modeling method based on similarity theory is proposed. The aerodynamic field of the 35 t/h layer combustion—composite combustion chamber—in the stoker boiler with staged combustion was evaluated. Further, a three-dimensional calculation model based on computational fluid dynamics (CFD) was used to simulate the aerodynamic field of the reformed boiler under normal operation, which facilitated convenience in the boiler design. Hot-wire anemometer and other instruments were used for the characteristic test of damper, a velocity field test in the furnace, wall wind test, temperature balance test at the outlet of the furnace, etc., and the law of motion for the flow field in the furnace was obtained. By analyzing the structure of staged combustion, the emission of nitrogen oxides and the combustion stability of a novel layer-fired boiler were studied. The calculated results are in excellent agreement with the experimental data. The results revealed that the combustion efficiency of the boiler and the reduction of nitrogen oxides were significantly improved by the staged combustion technology. There was no erosion on the water wall, and the flow velocity at the outlet of the furnace was uniform. This modeling method exhibits good adaptability to the combustion of stratified combustion boilers and is potentially useful for optimizing furnaces in a variety of applications.

Design and Performance Analysis of a Biomass Fueled Mono-Tube Boiler for Humid Air Turbine Cycle

Externally fired gas turbine (EFGT) is one of the few power generation configurations capable of utilizing biomass in its solid form without any additional equipment to convert it to liquid or gas. Due to its high thermal output capability for drying applications, EFGT is one of the most suitable configurations for the off-grid rural areas in Malaysia with abundant biomass waste and high demand of heat for crops drying. The main downside of EFGT is the necessity for high temperature heat exchanger which compromises the system feasibility due to the high cost and other technical challenges. This can be eliminated by the addition of steam in a configuration known as humid air turbine (HAT), thus, limiting the required temperature and allowing for the use of common low-temperature heat exchanger types. Several mono-tube steam boiler designs were compared to fulfil the required steam flow rate of 2 kg/min for the available EFGT system. Counter-flow design was found to be more suitable with its higher efficiency. The boiler was characterized experimentally at output steam flow rate range of 0.4-2 kg/min using off-cut waste wood from furniture industry. Maximum achieved boiler efficiency and specific fuel consumption were 73% and 0.29 kg/kWh, respectively.

Thermal-Hydraulic Calculation and Analysis on Evaporator System of a 1000 MW Ultra-Supercritical Pulverized Combustion Boiler with Double Reheat

A double reheat ultra-supercritical boiler is an important development direction for high-parameter and large-capacity coal-fired power plants due to its high thermal efficiency and environmental value. China has developed a 1000 MW double reheat ultra-supercritical boiler with steam parameters of 35 MPa at 605°C/613°C/613°C. Reasonable water wall design is one of the keys to safe and reliable operation of the boiler. In order to examine the thermal-hydraulic characteristics of the double reheat ultra-supercritical boiler, the water wall system was equivalent to a flow network comprising series-parallel circuits, linking circuits and pressure nodes, and a calculation model was built on account of the conservation equations of energy, momentum and mass. Through the iterative solving of nonlinear equations, the prediction parameters of the water wall at boiler maximum continue rate (BMCR), 75% turbine heat-acceptance rate (THA) and 30% THA loads, including total pressure drops, flow distribution, outlet steam temperatures, fluid and metal temperatures were gotten. The results of calculation exhibit excellent thermal-hydraulic characteristics and substantiate the feasibility of the water wall design of the double reheat ultra-supercritical boiler.

Analysis on the cause of crack in connection pipeline of subcritical boiler reheater

Several coal-fired thermal power boilers with the same sub-critical parameters in Mengxi area of Inner Mongolia have successively suffered from cracking and leakage failure events of reheater connecting pipes, most of which occur at chamfered back tool grooves on the inner wall grooves of pipe welding joints. In order to find out the cause of cracking, typical failure samples were intercepted for macro-morphology, microscopy, SEM, chemical composition, mechanical properties, wall thickness measurement analysis and design and operation data investigation of several boiler equipment. The results show that comprehensive factors such as deviation of burning coal type from design of boiler, automatic dispatching of AGC load in power grid, low nitrogen combustion modification and so on cause changes in boiler combustion conditions and operation, which results in excessive high input level of reheater cooling water, resulting in long-term alternating thermal stress and non-periodic vibration of straight pipe and elbow arranged after fine-tuning of refrigerant flow direction in reheater. Finally, thermal fatigue cracks are induced to initiate and propagate through the stress concentration area of the chamfered knife groove of the inner wall of pipe welded joints.

Study of TGM-94 boiler with variable feed water temperature using a calculation model

The article substantiates the need to test performance capability and effectiveness of a steam boiler in the new conditions under any changes in the regenerative heating circuit of the feed water in a steam turbine plant. Such changes may include: the displacement of steam extractions onto high pressure feed water heaters by the sun, by heat from biomass or garbage burning, or by steam from third-party sources. For this purpose we have developed a mathematical model of the steam boiler TGM-94 from steam turbine installation K-150-130. The model was created with Boiler Designer program. Verification of the calculated and experimental data provided by Krasnodar TTP showed sufficient convergence in both the steam-water and gas paths. We observed differences in the following temperatures: feed water temperature after the first stage of the economizer, flue gases and air temperature at the inlet to the furnace. The maximum difference between calculation and experiment here is 6 °C. We studied the boiler operation at a variable load, but with a constant temperature of the feed water equal to the nominal value of 230 °C. It was shown that in order to work in this mode, and in order to maintain the superheat temperature of the primary and secondary steam, it is necessary to turn on the flue gas recirculation smoke exhausters. We studied the operation of the boiler at a reduced feed water temperature. It turned out that such work leads to a decrease in steam production, if we keep the fuel consumption unchanged. In the case of sustaining steam production, it is required to assess the temperature state of the heating surfaces additionally due to a significant increase in the superheat temperature of both the primary and secondary steam.