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This paper presents the results of energy and economic analyses of a gas-fired CHP plant. The analyses were carried out for three variants of technical solutions to improve the thermal efficiency of the CHP plant. The fuel combustion process involves the generation of a large amount of heat. In addition, the heat is dissipated to the surroundings through the exhaust gas with a high temperature of 300÷350 °C. Therefore, to limit heat loss, a heat recovery system is used, which removes heat from the engine body and from the hot exhaust gases through a heat exchanger, allowing the exhaust gases to be cooled to a temperature of 100÷120 °C. In addition, heat is recovered from the oil cooling process and intercoolers. The recovered heat is usually supplied to the heating water in the district heating network. For the calculations, the temperature distribution of the return water from the district heating network during the year was assumed. First, the benefits of adding an additional economizer to pre-heat district heating water were analysed, Next, a heat recovery system was simulated to cool the flue gases to lower temperatures using an absorption heat pump or a compressor heat pump.

A passive wedge screen, thanks to its many functional and environmental advantages, has recently become a popular type of surface water intake for municipal and industrial purposes. The design solutions proposed in this paper for a passive wedge wire screen intake model and two different deflectors have been experimentally tested under conditions that can be considered as no-flow conditions at the hydraulic flume. There was only a slight flow associated with the operation of the screen, while there was almost no flow in the hydraulic channel itself, such that it would be considered a watercourse. A hydraulic analysis was carried out, including velocity distribution around the screen as well as the determination of head losses with or without deflectors installed inside the screen. Lower inlet and inflow velocities to the surface of the water intake reduce the risk of injury or death to small fish and fry as well as attracting pollutants understood as sediments, debris, and plant remains floating in the river. In order to achieve the lowest possible maximum inlet and inflow velocities at the highest possible intake capacity, it was necessary to equalize the approach velocity distributions. It was shown that by using the proposed deflectors, the approach velocity distributions were equalized and the maximum values of inflow and inlet velocities were reduced. A water intake screen with a deflector with an uneven porosity distribution equalized the approach velocities better than a deflector with equal openings, but the differences were small. Installing the wedge screen model reduced the maximum inlet velocity from exceeding 2 m/s to a value of 0.08 m/s, and after installing deflectors with equal and unequal openings to values of 0.06 m/s and 0.05 m/s, respectively. In addition to laboratory tests, the paper describes the numerical simulations performed in ANSYS Fluent software. The results of the simulations made it possible to obtain a broader study, as well as to compare the velocity values obtained at the measuring points during the laboratory tests. [ABSTRACT FROM AUTHOR]

Thick-wall components of the thermal power unit limit maximum heating and cooling rates during start-up or shut-down of the unit. A method of monitoring the thermal stresses in thick-walled components of thermal power plants is presented. The time variations of the local heat transfer coefficient on the inner surface of the pressure component are determined based on the measurement of the wall temperature at one or six points respectively for one- and three-dimensional unsteady temperature fields in the component. The temperature sensors are located close to the internal surface of the component. A technique for measuring the fastchanging fluid temperature was developed. Thermal stresses in pressure components with complicated shapes can be computed using FEM (Finite Element Method) based on experimentally estimated fluid temperature and heat transfer coefficient

A power plant with additional water pressure tanks was proposed. The maximum rise in the block electric power resulting from the shut-off of low-pressure regenerative heaters was determined. At that time, the boiler is fed with hot water from water pressure tanks acting as heat accumulators. Accumulation of hot water in water tanks is also proposed in the periods of the power unit small load. In order to lower the plant electric power in the off-peak night hours, water heated to the nominal temperature in low-pressure regenerative heaters is directed from the feed water tank to pressure tanks. The water accumulated during the night is used to feed the boiler during the period of peak demand for electricity. Pressure accumulators are proposed to be used for the rapid start-up of the boiler from a cold state. The evaporator of the boiler is filled at the beginning of start-up with hot water from the accumulators. Drops in the power block electric power were determined for different capacities of the tanks and periods when they are charged. The tanks may also be used to ensure a sudden increase in the electric power of the unit that is operating in the automatic system of frequency and power control (in Polish: ARCM).

Allowable rates of fluid temperature changes in critical elements of supercritical steam boilers were determined assuming a quasi-steady state of temperature distribution in pressure components. A method was proposed for monitoring the thermal stresses in the critical pressure components. [ABSTRACT FROM AUTHOR]

Superheaters are high-temperature cross-flow heat exchangers. Steam flows inside the tubes, and the flue gas outside in a direction perpendicular to the axes of the tubes. However, they differ very substantially from the other heat exchangers operating at low temperatures. Superheaters are characterized by complex flow system and high tube walls temperature. Superheaters are among the most exposed to damaging pressure elements of steam boilers. Damage to the superheater causes about 40% of emergency shutdowns of boilers. The paper presents the boiler superheater model with distributed parameters, which is used to determine on-line the degree of superheater fouling by ash. [ABSTRACT FROM AUTHOR]

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The paper presents research to develop a complete system for recovering, storing and utilising the thermal energy of the knocked-out moulding sand. The cooling of the moulding sand is slow and, therefore, moulding sand cannot be used in a regeneration station and returned to the foundry process quickly. The moulding sand cooling process can be accelerated, and the recovered heat can be used in other energy-intensive processes in the foundry. As for now, the heat recovery methods or the ways of the heat further use are unknown. This paper presents the concept of a heat recovery system that allows to utilise the heat contained in moulding sand knocked out of large moulds at temperatures between 350 and 400 °C. The permissible moulding sand temperature at the inlet to the regeneration station should not exceed 90 °C. It is assumed that the moulding sand will be cooled with water in two vertical cylindrical tanks where heat exchangers with finned tubes will be placed. Using numerical modelling, the design of a heat exchanger for moulding sand cooling was selected. The capacity of the developed heat exchanger is 600 kW. Numerical analyses and experimental tests confirmed that the heat exchanger can absorb all the heat from the moulding compound and cool it down to 90 °C within 6 h. Implementing the developed system will reduce the foundry's CO2 emissions by 329 tonnes annually. • The knocked-out moulding sand contains large amounts of waste heat. • It is possible to recover and utilise waste heat from the knocked-out moulding sand. • CFD modelling of the moulding sand cooling process was performed. • The FEM was used to perform a thermal-strength analysis of the heat exchanger. • A system for recovering waste heat from knocked-out moulding sand was developed. [ABSTRACT FROM AUTHOR]

A heat recovery system from flue gas increases the overall efficiency of a district heating or CHP plant, as the system recovers the waste energy contained in the flue gas at the chimney outlet. This makes it possible to increase thermal energy production with the same fuel consumption. A method for calculating the thermodynamic parameters of municipal waste incineration plants was developed as part of the work carried out. The mathematical models prepared made it possible to analyse the impact of the heat recovery system from flue gas on technical and economic parameters and the environment, including, among other things, an estimate of the annual amount of heat recovered, the amount of additional electricity consumed, the amount of condensate treated, the estimated capital expenditure, operating profits and operating costs. The results of the analyses were the basis for designing and constructing a heat recovery system from flue gas equipped with a condensation heat exchanger for the municipal waste incineration plant in Cracow. The calculation results were compared with the measurement results obtained during the test run of the constructed installation. • Technical description of the heat recovery system from flue gas. • A method for calculating the parameters of municipal waste incineration plants. • The impact of the heat recovery system on technical and economic parameters. • An analysis of the Thermal Waste Treatment Plant operation. • The calculation results were compared with experimental data. [ABSTRACT FROM AUTHOR]