Heat Recovery Steam Generator Research Articles

Thermodynamic study of different configurations of gas-steam combined cycles employing intercooling and different means of cooling in topping cycle

Various options for improving the performance of gas/steam combined cycle, the performance enhancement can be achieved by increasing the turbine inlet temperature and/or increasing the cycle pressure ratio along with intercooling for reducing compression work and reheating for increasing the expansion work. The present paper analyses eight novel configurations of the intercooled gas turbine based combined cycles having the gas turbine blade cooled using closed loop cooling scheme. Combined cycle configurations differ in respect to cooling medium being steam or ammonia-water, intercooling, reheating, single/dual/triple pressure heat recovery steam generator, steam turbine, and ammonia water turbine. The comparative evaluation of combined cycle arrangements is based on thermodynamic modeling using first law and the second law of thermodynamics for the inlet temperature to turbine of 2000 K and ambient temperature of 303 K. Study aims at furnishing results for understanding the implications of modifications on the cycle performance. The results show that maximum 1142 kJ/kg of work is obtained for ammonia concentration of 0.6 while the maximum cycle efficiency of 53.87% and second law efficiency of 58.46% is obtained for ammonia concentration of 0.7 at cycle pressure ratio of 40 for combined cycle with triple pressure heat recovery vapor generator having ammonia-water cycle at high pressure& intermediate pressure and Rankine cycle at low pressure.

ASPEN dynamics simulation for combined cycle power plant – Validation with hot start-up measurement

Since the beginning of energy market liberalization, shutdown and start-up phases of thermal power plants have acquired greater importance. Dynamic simulation is a helpful tool due to its possibility of predicting the behaviour of the power plant with a good degree of accuracy. This paper goes into the details of the hot start-up phase of a combined cycle power plant with three-pressure level heat recovery steam generator, analysing the capability of the software ASPEN Plus Dynamic through a dynamic comparison between the numerical results and the real operation data. The developed model is built according to the design data of an actual plant including heat exchangers, pipes, turbines, valves, pumps and so on. Good agreements between measurement and simulation results, with some discrepancies in the first phase of the start-up, have been found and then discussed. Best deviation values are obtained for the temperature where the maximum relative error is 3.62% in the re-heater section. Worst deviation values are obtained for the pressure where the maximum relative error shown is 10.8%. Further possible improvements of the model and future applications are suggested.

Effect of Increasing Sea Water Temperature on Performance of Steam Turbine of Muara Tawar Power Plant

Muara Tawar Power Plant is located on the coast of Bekasi, West Java, Indonesia. Along with the economic development, there are plans to do reclamation the sea around Muara Tawar Power Plant and build around it as a port and industrial estate. This could potentially lead to an increase in sea water temperatures. This paper aims to determine the effect of increasing sea water temperature on the performance of steam turbine 1.4 in Muara Tawar Power Plant, which uses sea water as a condenser cooling medium. The intended performance is the output power of the steam turbine, the condenser pressure and the system efficiency. Steam turbine 1.4 has 225 MW installed output power, supplied from 3 HRSG (Heat Recovery Steam Generator).Analysis of the effect of sea water temperature rise on steam turbine performance is carried out by using the cycle-tempo software. The main equipment of steam turbine is modeled in cycle-tempo, then model is validated by comparing with design data. Varies sea water temperature then is inputted on model in order to obtain the output power of steam turbine, condenser pressure and system efficiency. The results show that for every 1˚C increase in condenser cooling water temperature extracted from seawater near the plant, the output power of the plant decreased by about 0.171%, the condenser pressure increased by about 5.146%, and the system efficiency decreased by about 0.168%.

Deactivation mechanism of activated carbon supported copper oxide SCR catalysts in C2H4 reductant

Current state‐of‐the‐art NH3‐SCR technology based on vanadium catalysts suffers problems associated with NH3 slip and poisoning of the catalyst and blockage of heat recovery steam generators (HRSG). If environmentally‐friendly catalysts capable of efficient operation at lower temperatures could be developed that used a reductant other than NH3, the issues with current state‐of‐the‐art SCR could be significantly lessened. Hence, in this study, activated carbon (AC) supported copper oxide‐based catalysts for SCR while using C2H4 as a reductant was discussed. Reaction testing of catalysts demonstrated high initial NO conversion with steeply declining activity over 2 h of testing when C2H4 was used as the reductant; in comparison, with the same catalyst and NH3 as the reductant, stable, long‐term NO conversion was achieved, but at a lower rate than the initial reactivity with C2H4. As a consequence, catalyst characterization studies were performed to assess deactivation mechanisms when C2H4 was the reductant. These studies included x‐ray diffraction, BET surface area and porosity, temperature programmed reduction, scanning electron microscopy, Raman spectroscopy and x‐ray photoelectron spectroscopy of both fresh and deactivated catalysts. The analytical results showed the surface area and porosity of the catalyst remained unchanged and the initially highly‐dispersed Cu species became agglomerated and more crystalline during reaction testing. Furthermore, carbon black was also detected on the catalyst surface after testing, presumably formed during the decomposition of C2H4. Both agglomeration of the active Cu species and blockage by carbon deposits would decrease the availability of active sites and lead to decreased catalytic activity.

Heat recovery and optimizing design of furnaces in the gasoline-kerosene units of Tabriz Oil Refining Company

One option for heat recovery and decrease in consumption of fossil fuel burning in order to power generation and mitigation the carbon dioxide (CO2) emission in the atmosphere is the application of heat recovery steam generator (HRSG). It is studied here from viewpoints of techno-economic analysis, process optimization, and environmental impact. This paper is focused on the design of an HRSG, aiming to optimize the plant efficiency in gasoline-kerosene units, Tabriz petroleum refinery, Iran, through heat recovery from the exhaust (flue) gases of the furnaces’ stacks in these units. Heat transfer and pressure drop calculations are done based on a methodology of maximizing the value of profit in terms of the approach points in the HRSG. The results showed that the HRSG in its optimum design can generate steam (42 bar and 390 °C), with a maximum profit of 6,650,000 $ during a period of 10 years operation with a temperature of 210 °C for flue gases exiting the HRSG at approach point of 14.3. Moreover, applying the steam generated by the HRSG in the plant, it can be saved 1500 kg/h natural gas from burning which decreases from emitting a considerable amount of CO2 in the atmosphere.

Converting Zubair oil field permanent power generation from single cycle into combined-cycle with plant exergy analysis

The combined-cycle power plant is the effective way to increase power and thermal efficiency which can rise thermal efficiency up to 50% corresponding to low heat value of the fuel (LHV). This study focused on converting Zubair Oil Field Gas turbine (ALSTOM GT13E2) from single cycle into a combined cycle power plant. Models suggestion design have been presented with back-pressure steam turbine by Cycle-Tempo (5.1) thermodynamics simulation program, which presents value diagram and exergy flow diagram both are useful to understanding the thermodynamic performance of complicated systems.The result of exergy analysis explicate that huge amount of exergy loss firstly occurs in gas turbine combustor (about 60% due to high irreversibility), and heat recovery steam generation (HRSG) is the second major exergy loss in combined cycle power plant (about 30%) recently apparatus concepts less than 10% of exergy (like compressors and expanders). Also, in this study explained the effect of changing the ambient temperature on the performance of power plant by using four temperature parameters on the four simulation models at constant compression ratio. The results were the increase in gas turbine temperature inlet led to decrease the net power output of the CCPPs. Thermal and exergy efficiencies increase when ambient temperature increase due to growth turbine inlet temperature but this temperature restricted by creep rupture and thermal fatigue for combustor parts and turbine blades metal. Maximum thermal and exergy efficiencies can be reached to 55.74, 53.28% respectively at worst ambient temperature. The calculation results in this study were compared with two previous studies, with considerable differences in input parameters of the gas turbine and steam turbine also, the types of the gas turbine models. finally, the results showed acceptable agreement.

Conventional and enhanced thermodynamic and exergoeconomic analyses of a photovoltaic combined cycle with biomass post firing and hydrogen production

Due to the finite nature of fossil fuels and their unsustainable function in the power production industry, a photovoltaic combined cycle with biomass post firing and hydrogen production is proposed and assessed with conventional and enhanced (avoidable and unavoidable) exergy and exergoeconomic analyses. It is observed that increasing the compressor pressure ratio increases the CO2 discharge rate, the system exergy destruction rate, and the exergoeconomic factor of the cycle, and decreases the exergy efficiency, the natural gas flow rate, the exergy destruction cost rate and the system unit product cost. Further, the energy efficiency is optimized by adjusting the compressor pressure ratio. Increasing the area of the photovoltaic thermal system decreases the energy and exergy efficiencies and increases the unit product cost of the system. Hydrogen injection to the combustion chamber is an alternative for using the product hydrogen. This operation decreases the CO2 discharge rate, the exergy destruction rate in the combustion chamber, the system product cost and the energy efficiency. A comparison of the results of conventional and enhanced analyses shows that they have different implications about the optimization of the post combustion chamber, the heat recovery steam generator, and the pump. With conventional analyses, the post combustion chamber and the pump should be considered for investment cost decreases and the heat recovery steam generator for quality improvement. But the enhanced analyses lead to opposite conclusions.

Numerical study of heat transfer characteristics of semi-coke and steam in waste heat recovery steam generator for hydrogen production

With the steam obtained from the waste heat of high temperature semi-coke, the hydrogen production through gasification method is considered more commercially. The heat transfer of semi-coke bed and steam was investigated using an unsteady convection heat transfer three-dimensional model of semi-coke. The effects of particle size, steam flow and particle bed thickness on heat transfer characteristics were considered. The particle temperature calculated by three-dimensional model was in good agreement with the corresponding particle temperature of experiment. The heat transfer characteristics of single particle, the particle temperature, the amount of heat recovery and the heat flux were investigated. The results show that, in the first 10 min of the heat transfer of semi-coke bed and steam, the bottom particle temperature decreases rapidly, but the top particle temperature is almost unchanged. The heat transfer rate evolution of the single particle in different positions is revealed. The heat transfer rate evolution of the bottom particle is different from that of the middle particle and top particle, and the heat transfer rate evolution of middle particle is similar to that of the top particle. The particle size, the steam flow and the particle bed thickness have great influence on the heat transfer mechanism of semi-coke and steam, and the 7.5 kg/h is considered to be the best steam flow for heat recovery. The intrinsic heat transfer mechanism between semi-coke bed and steam was revealed.

Modeling of fractal heat conduction of semi-coke bed in waste heat recovery steam generator for hydrogen production

With the steam obtained from the waste heat of high temperature semi-coke, the hydrogen production through gasification method is considered more commercial. In order to improve the efficiency of waste heat recovery, the fractional model for heat conduction of semi-coke bed in waste heat recovery process was established. The non-destructive CT was employed to obtain the inner morphology of semi-coke bed and the image binarization processing was used to segment the CT image. With the MATLAB program, the box-counting method was used to calculate the fractal dimension of semi-coke bed. The fractional model for heat conduction of semi-coke bed was established by the fractal theory. The results showed that, the CT image and bit binary image of semi-coke bed can really reflect the inner morphology of semi-coke bed, and the inner morphology of semi-coke bed can be regarded as a fractal medium. The fractal dimension of semi-coke bed is 1.7537, which is very close to golden mean, 1.618, this could be the optimal structure for the heat conduction of semi-coke bed under the condition of natural accumulation. The one-dimensional heat conduction fractional equation of semi-coke bed was established and it can be accurately solved by fractal complex transformation and traveling wave transformation.

Multi-objective Design of a Biomass-based Polygeneration for Iron and Steel Manufacturing

Iron and steel manufacturing is considered a major contributor to the global carbon emission and energy-intensive industry. To sustainably produce iron and steel, various approaches have been explored to generate the needed power to support the production while mitigating the carbon dioxide emission. One of the viable approaches is the integration of a biomass-polygeneration system to produce biochar and other energy streams needed by the iron and steel manufacturing plant. A polygeneration system is composed of a combination of various existing technologies which seeks to recover wasted energy and to reuse by-products through process integration, thus, improving the overall thermodynamic efficiency of the system. In designing such complex systems, multiple objectives should be considered to assimilate the real-life requirements of the system. However, recent studies on the design of polygeneration system for iron and steel industry used a single-objective approached which may not consider the trade-offs between multi-objectives. Hence, this study proposes to design a biomass-based polygeneration system using a multi-objective approach employing fuzzy linear programming (FLP) model. The FLP model allows partial satisfaction of multi-objectives through the use of linear membership functions. A case study is presented involving biochar production from torrefaction, pyrolysis, and gasification together with power and heat production. The results indicate the optimal polygeneration process network consisting of a gas turbine for the generation of power, a heat recovery steam generator attached to the gas turbine for the heat generation, a gasifier for syngas, and torrefaction for biochar production. The developed model aims to aid engineers and managers in cost-effectively integrating a biomass-based polygeneration system in iron manufacturing.

Experimental Aerodynamic Investigations of the 100-MW Two-Shaft Gas Turbine Unit Exhaust Duct

The article describes the results from experimental investigations into the exhaust duct aerodynamics of a stationary two-shaft gas turbine unit (GTU) intended for operation in a combined-cycle plant equipped with a heat-recovery steam generator. The experiments were carried out at the Kirillov Turbine Construction Laboratory of Peter the Great Polytechnic University (SPbPU). The aim of investigations was to experimentally determine the 3D flow structure in the diffuser–exhaust hood flow path and its integral characteristics during operation in combination with the topping turbine stage. The pressure recovery factors and the energy loss coefficients in the diffuser and in the exhaust duct are determined. The circumferential and radial distributions of the 3D flow parameters in the diffuser inlet section are presented. Based on the experimental investigation results obtained for the exhaust duct operating jointly with the topping stage, the main energy loss sources in the duct are determined, and recommendations for improving its aerodynamics are given. A comparative analysis of the exhaust duct’s integral aerodynamic characteristics and of the flow structure parameters obtained during the tests with and without the topping stage is carried out. The results obtained from the comparative analysis of the data obtained in the experiments with the connected topping stage and with the isolated exhaust duct were used for working out recommendations on modeling the stream in the flow paths of two-shaft GTU exhaust ducts.

Multi-objective linear regression based optimization of full repowering a single pressure steam power plant

Full repowering of Be'sat steam power plant has been studied in this work. The methodology is used to simulate the new cycle according to its principal specifications and to optimize it based on the objective functions. Objective functions are electricity cost per kWh and exergy efficiency. These parameters are functions of the pinch and approach point temperature differences at high and low pressure points and at the pre-heater in the heat recovery steam generator (HRSG), steam turbine inlet flow rate, gas turbine (GT) isentropic efficiency, air compressor isentropic efficiency and compressor pressure ratio. Finally, considering the introduced objective functions, it is tried to achieve the most optimized techno-economic characteristics for Be'sat power plant repowering cycle using the genetic algorithm with two scenarios of single and multi-objective optimizations. The results show that the efficiencies of the repowered cycle are 52.59% and 51.3% for two cases of unfired and fired duct burners, respectively.

Configuration of Evaporators for Once-Through Heat Recovery Steam Generators of Combined-Cycle Units

Various designs are examined of evaporators for horizontal or vertical once-through heat recovery steam generators (HRSG) of combined-cycle units. Special attention is given to the Benson boilers manufactured by Siemens, which are most widely used now. Vertical HRSG with evaporators having horizontal heating surface sections are also analyzed. Their advantages and disadvantages are outlined. It is demonstrated that HRSGs with vertical heating coils provided with equalizing headers are more advantageous. The equalizing headers are connected with stubs to bottom U-bends of the coils. All heating surfaces are drained by gravity. The temperature conditions of this evaporator were investigated in a GTU load range of 25–100%. It has been found that partial load operation results in poorer heat transfer due to the boiling crisis. However, the maximum temperature jump in the post dryout region will be approximately 25–30°С, which is quite acceptable for reliable operation of low-alloy steel tubes. Assessment of the flow stability at the precrisis conditions demonstrates that the two-phase flow in the evaporator is stable over the applicable load range of HRSG. The calculations were performed for the evaporator without an orifice at the coil inlets. On the whole, the thermal-hydraulic operating conditions of these boilers are much better than those of Benson boilers. From the construction standpoint, a coil evaporator with equalizing headers is simpler and less metal intensive. A quite high liquid velocity is kept at all loads. Dynamic properties are also advantageous, since the material and the geometry of metal intensive elements of the evaporator, such as separators and water tanks, have been selected to improve performance of the overall HRSG.

Investigation Tests of the P-134 Heat-Recovery Steam Generator Used as Part of the PGU-230T Combined-Cycle Power Unit

Investigation tests of the P-134 heat-recovery steam generator (produced by PJSG Zio-Podolsk) used as part of the PGU-230T combined-cycle power unit at the Chelyabinsk combined heat and power plant no. 3 (CHPP-3) were carried out, as a result of which experimental data on the steam generator thermal parameters have been obtained, and adequacy of the thermal–hydraulic design analysis model developed by PJSG ZiO-Podolsk has been confirmed. A description of the heat-recovery steam generator is given along with schematic arrangements of experimental instrumentation, test conditions and techniques, and experimental data processing methods. A procedure and computer program for estimating the steam generator thermal parameters, and a procedure for reducing the test results to design conditions are elaborated. It has been determined that the total thermal power of heating surfaces in the steam–water path deviates from the steam generator total thermal power directly measured at the boundary balance sections by no more than 0.84%. The steam generator thermal power values determined with reference to the steam–water and gas paths differ from each other by no more than 1.7%. The steam generator thermal power obtained in the tests differs from its design value by no more than 2.4%, and it should be noted that its value measured in all operating modes was higher than its design value. The design thermal power values of the high-pressure loop heating surfaces reduced to the test conditions differ insignificantly (and toward increasing) from their actual values. The obtained results demonstrate that the analysis models can be used for reducing the test results to the heat-recovery steam generator operating conditions (parameters) at which the conformity of their values is established for confirmation (assessment) purposes, in particular, in carrying out warranty tests. It has been shown that the heat recovery steam generator’s thermal power reduced to the warranty conditions that was obtained in all test modes is somewhat higher than the design thermal power under the warranty conditions.

Various Approaches to Thermodynamic Optimization of a Hybrid Multi-effect Evaporation with Thermal Vapour Compression and Reverse Osmosis Desalination System Integrated to a Gas Turbine Power Plant

This paper investigates the simulation of a hybrid desalination system composed of multi-effect evaporation with thermal vapour compression desalination (METVC) and reverse osmosis (RO) plant. The hybrid desalination system is also integrated with a gas turbine power plant through a heat recovery steam generator (HRSG). First, a comprehensive Thermodynamic model for HRSG, METVC, and RO are developed for predicting thermal behaviour of hybrid desalination system. Depending on the interconnection between input and output streams of METVC and RO, six configurations are proposed, and their results are compared in two different scenarios. In the first scenario, METVC desalination production is fixed at its maximum capacity of 70000 m3/day. The heat potential of power plants is fully extracted at maximum capacity of production of METVC. In the second scenario, METVC desalination production is not fixed. The limitation on the total production of the desalination plant (METVC+RO) is imposed as a constraint to the optimization problem. The results show that, regardless of the scenario under consideration, cconfiguration 1(the outlet water of the cooling system in METVC has been used for the feed water of the RO system) has the minimum energy consumption as well as maximum exergy efficiency.

Improving Flexibility and Economic Efficiency of CCGT Units’ Operation in the Conditions of the Wholesale Electricity Market

The issues of improving flexibility and operation modes of combined-cycle plants with three-pressure heat-recovery steam generators (CCGT with HRSG) are considered in the conditions of the wholesale electricity market. Operation modes of high-performance CCGT units, which were designed mainly for the basic operation mode with a minimum number of starts and load variations are significantly different from it due to the lack of regulatory capacities in power systems. The increasing CCGT unit fractional load running time, emerging role of ramping to the minimal possible load, and expediency of involving the CCGT unit to adjust the frequency and power in the power system make it necessary to extend their adjustment load range limits. The article analyzes the possibilities and the need for maximum CCGT ramping during the night-time valley from a technical and economic point of view. The factors limiting the CCGT load range are obtained computationally and experimentally. The ways to reduce the technological minimum CCGT load are considered by heating the compressor inlet air, bypassing part of the compressed air to its inlet, and enhancing its flow control using inlet guide vanes (IGV) as well as combining these methods. The influence of the electricity price in the day-ahead market on the optimal generating capacity load is analyzed. The optimization of the CCGT operating modes in the conditions of the wholesale electricity market is carried out with allowance for the developed load range extension methods.

Design/off-design performance simulation and discussion for the gas turbine combined cycle with inlet air heating

A novel method for the combined cycle retrofitted with compressor inlet air heating (HEAT) process is proposed in this work for part load performance improvement. The performance of the new cycle is researched with two regulations with HEAT and compared with another two strategies with compressor inlet guide vane (IGV). For the novel method, the compressor inlet air is preheated by part of the exhaust flue gas from the heat recovery steam generator. Moreover, comparation result indicates that the novel strategy with HEAT to maintain design turbine inlet temperature (T3) and then to keep turbine exhaust temperature (T4) at its maximum value (HEAT-T3-T4) is suggested for load arrangement. If being compared with the cycle using IGV control to maintain design T3 then keep extreme T4 (IGV-T3-T4), a maximum combined cycle efficiency increment as 1.7% pt. could be obtained by the cycle with HEAT-T3-T4. Both energy analysis and exergy analysis are given in this paper. The simulation results indicate that higher compressor outlet temperature (T2) decreases the extra exergy destruction during combustion, so that the performance of the cycle with HEAT is improved. Meanwhile the specific work of each cycle has also been presented. Furthermore the pressure loss affection of the compressor inlet air heat exchanger on the combined cycle performance is investigated in range of 0%–5%. Each 1% pressure loss is calculated to decrease 1.4% on the design power output, and 0.25% pt. on the combined cycle efficiency, which will weaken the performance improvement. To summarize, this paper proposes a novel method for the combined cycle power output adjustment to obviously improve its part load efficiency. This innovative solution has never been suggested before and it could be combined with other methods for better result.

Thermo-economic analysis of a heat recovery steam generator combined cycle

A significant amount of energy gets lost through the exhaust of simple gas turbine plants, more often than not, this energy can be used to run another power cycle or a combined heat and power setup, leading to an increase in the overall efficiency of the plant, reduce air pollution and energy wastage. In this study, a retrofitted performance analysis of incorporating a steam power cycle to the existing gas turbine cycle in Delta IV power station is carried out, the analysis is carried out using first law of thermodynamics and energy cost comparison to describe the effect of combining both cycles on power output, thermal efficiency and energy cost. Operating data were obtained from existing gas thermal plant in Ughelli (Delta IV) and steam thermal plant in Lagos (Egbin). Preliminary assessment shows that power output increases by a further 51.5MW, thus raising the overall combined efficiency to 41.85%. Analysis on cost savings accruable from incorporating a heat recovery steam generation was also done and significant savings in cost was obtained. Keywords: combined cycle, HSRG, gas turbine, steam turbine, energy cost

EVALUATION OF THE PERFORMANCE AND ENERGY EFFICIENCY OF INTEGRATED SOLAR COMBINED CYCLE POWER PLANT

Abstract: An integrated solar combined cycle (ISCC) composed of a triple-pressure natural gas combined cycle and parabolic trough collector solar field is investigated in this paper. The purpose is to study and evaluate the performance of the cycle when the solar heat injected into the heat recovery steam generator of the steam cycle. Thus, a thermodynamic model of the proposed ISCC plant has been developed in Mathcad environment to simulate and analyze the cycle performance ate different seasons of the year. It has been found that the solar energy can generate steam that can be used to increase the power output of the steam cycle from 182 MWe to 237 MWe with an increase of 30% from reverence value. This can achieve an annual reduction in CO2 emission of 75000 tons/year.

Performance Evaluation of a Combined Heat and Power Plant in the Niger Delta of Nigeria

This research presents the performance assessment of a combined heat and power plant operating in the Niger Delta region of Nigeria. The main focus is to evaluate the performance parameters of the gas turbine unit and the waste heat recovery generator section of the combined-heat-and-power plant. Data were gathered from the manufacturer’s manual, field and panel operator’s log sheets and the human machine interface (HMI) monitoring screen. The standard thermodynamic equations were used to determine the appropriate parameters of the various components of the gas turbine power plant as well as that of the heat exchangers of the heat recovery steam generator (HRSG). The outcome of all analysis indicated that for every 10C rise in ambient temperature of the compressor air intake there is an average of 0.146MW drop in the gas turbine power output, a fall of about 0.176% in the thermal efficiency of the plant, a decrease of about 2.46% in the combined-cycle thermal efficiency and an increase of about 0.0323 Kg/Kwh in specific fuel consumption of the plant. In evaluating the performance of the Waste Heat Boiler (WHB), the principle of heat balance above pinch was applied to a single steam pressure HRSG exhaust gas/steam temperature profile versus exhaust heat flow. Hence, the evaporative capacity (steam flow) of the HRSG was computed from the total heat transfer in the super-heaters and evaporator tubes using heat balance above pinch. The analysis revealed that the equivalent evaporation, evaporative capacity (steam flow) and the HRSG thermal efficiency depends on the heat exchanger’s heat load and its effective maintenance.