Regenerative Preheater Research Articles

Experimental evaluation of an ORC-CHP architecture based on regenerative preheating for geothermal applications

The Organic Rankine Cycle (ORC) can be applied to generate power from low-temperature heat sources and thus supports a sustainable energy system. This paper contributes to ORC development, particularly for geothermal applications, to increase competitiveness of the technology. To this end, new plant architectures based on regenerative preheating are being investigated. The concept of regenerative preheating is investigated in literature by numerical studies and its thermodynamic and economic performance is predominantly evaluated positively. However, regenerative preheating has not yet been realized in experimental ORC test rigs or commercial products. For this purpose, a novel ORC test rig is designed, constructed and commissioned. For evaluation purposes, the regenerative preheating concept is compared to a standard ORC configuration. As a result, a 9.9% higher net thermal efficiency is achieved with regenerative preheating, while the net power output is equal to the one achieved with the standard configuration. This result is particularly important for combined heat and power (CHP) generation due to the reduced cooling of the heat source. In order to evaluate this concept for CHP applications, a novel ORC-CHP architecture based on regenerative preheating is experimentally compared to three state-of-the-art ORC-CHP concepts. Moreover, three different supply and return temperatures of the district heating system (DHS) are considered. The results reveal that the novel architecture, in combination with low- and medium-temperature DHS, leads to an increased part-load performance and a wider operating range. This enables up to 9.4% increase in annual net electricity production, which accounts for additional revenues of 4.56million € in the case of a typical geothermal project. Thus, it can be concluded that this novel ORC-CHP architecture is beneficial from a technical perspective and also promising in terms of economics.

Performance analysis of ammonia decomposition endothermic membrane reactor heated by trough solar collector

In order to promote the engineering application of ammonia-based solar thermal storage systems, a one-dimensional model of an ammonia decomposition endothermic membrane reactor based on actual light condition is established by applying finite time thermodynamics. The reactor is heated by a trough solar collector and equipped with a regenerative preheater, and effects of four parameters including ammonia molar flow rate, ammonia preheated temperature, permeation zone pressure and light intensity on the total heat absorption rate, entropy generation rate and system efficiency are analyzed. The results show that the permeate pressure and light intensity affect the system performance significantly. When the permeate pressure reduces from 1 bar to 0.1 bar, the total heat absorption rate, the system efficiency and the entropy generation rate increase by 32.3%, 22.3% and 16.4%, respectively. When the light intensity increases from 800 W/m2 to 1200 W/m2, the heat absorption rate and the entropy generation rate increase by 53.8% and 38.2%, respectively. The results obtained in this paper provide some guidance for the practical engineering application of ammonia decomposition heat endothermic membrane reactors.

Rotary reverse flow reactor vs. adiabatic reactor with regenerative preheating - Design and comparison

The autothermal catalytic-combustion systems are commonly used for the purification of waste air streams contaminated with low concentrations of volatile organic compounds (VOC). Within this type of devices, the reverse flow reactors (RFR) are known to be more efficient than systems employing recuperative (surface) heat exchangers to preheat the waste air stream with the lean air effluent from the catalytic incinerator. The advantage of the RFR is basically due to the regenerative heat-exchange mechanism, provided by the inert and catalytic solids inside the unit.As an alternative, the regenerative mechanism of preheating can be achieved by an independent heat exchanger, which coupled to a catalytic reactor could be expected to produce similar performance as the RFR.In this context, this contribution is devoted to analyse comparatively the performances of a rotary reverse flow reactor (RRFR) and a system comprising a rotary regenerative heat-exchanger and a catalytic reactor (RHE-SR system) for the treatment of a waste air stream contaminated with ethanol and ethyl acetate, by means of mathematical simulation. Both alternatives are assumed to be composed of monoliths with square channels. A strategy of design for both systems suitable for their comparison is proposed, attending to a range of VOC concentration in the waste stream. Both alternatives can be regarded as being suitable options to carry out the target. However, the resulting designs show clear advantages in favour to the RRFR, as this alternative requires a significantly more compact equipment than the RHE-SR does and, besides, it allows to be operated under a wider range of the rotational speed, which is the main control variable once the systems are operating.

Modeling for Leakages Calculation in Design of Rotary Regenerative Preheater

Pressure and carryover leakages are inherent in operation of rotary air preheater due to regenerative heat transfer mode.18 leakage flows take place in multiple sites,including peripheral and axial pressure leakages interacted with each other,which formulate a complex network of gas flow in tri-sectional rotary air preheater.The objective of this paper is to provide a comprehensive modeling for leakages calculation in the design of the preheater.It is based on the leakage mass flow rates governed by the matrix rotation and pressure drops across the seals,together with mass and energy balance equations in mixing processes.Air and flue gas temperature and pressure inlet/outlet the preheater,primary and secondary air mass flow rates outlet the preheater,flue gas mass flow rates inlet the preheater,as well as seal clearance are considered as known in the model,the leakage mass flow rates and directions,and actual gas flow rates through the matrix are determined by solving pressure leakage and mixing equations.For a tri-sectional rotary air preheater of a 600 MW boiler,pressure and carryover leakages are simulated in various seal settings,the results clearly show that primary air leakage accounts for about 75% of the amount of air leakage,the actual primary flow through the matrix accounts for 72% to 86% of the inlet flow,changes in seal settings have more impact on primary air system than secondary air system,ignore of flue gas carryover leakage,done as in National standards,can cause the measured air leakage rate 0.85% lower than the actual value.

DEVELOPMENT OF A THERMALLY HOMOGENEOUS GASIFIER SYSTEM USING HIGH-TEMPERATURE AGENTS

DEVELOPMENT OF A THERMALLY HOMOGENEOUS GASIFIER SYSTEM USING HIGH-TEMPERATURE AGENTS

Useful work and the thermal efficiency in the ideal Lenolr cycle with regenerative preheating

In the existing thermal engine concepts negative work transfer (usually needed to drive a compression process) is supplied by the work produced by the engine itself. The remaining difference (i.e., the net work transfer) becomes the useful work, since it is available for external consumption. The thermal efficiency is the parameter that compares this against the heat input into the system. It forms the main optimization parameter in any engine design. The objective of the present study is to show that for the case of the Lenoir cycle with regenerative preheating the entire positive work is available for external consumption, since the negative (i.e., the compression) work is supplied by the atmospheric air. Not only this, but, during the compression process and due to the pressure difference across the two sides of the moving piston, an additional (useful) work transfer may be generated. Thus, the proposed power plant may be considered as a combination of a thermal engine and a wind turbine. In the ideal cycle limit (at least), the total amount of useful work exceeds the heat entering the system. This leads to the definition of a new parameter for the efficiency (called the technical efficiency), which compares the combined positive work transfer (i.e., the useful one) against the heat entering the system and which may exceed the 100% level.

Corrosion Assessment of Regenerative Preheaters in Oil-Fired Power Plants

Abstract Electrochemical techniques for on-line corrosion monitoring were used to study low-temperature corrosion of regenerative air preheaters in oil-fired power stations. The cause of metallic corrosion on the studied structure was condensation of sulfuric acid (H2SO4) from flue gas on the heat-exchanger surfaces. A corrosion probe was designed and installed. Results under various operating conditions were evaluated. Measurements obtained showed the dynamics of this industrial system and the benefits of real-time monitoring in understanding corrosion behavior of acid condensation.

Supercritical heat pump cycles

Supercritical heat-pump cycles suited for high-temperature heat generation and in which heat is delivered in the form of sensible heat of a high-pressure fluid are examined and their energy performance is evaluated. The main variables governing the energy efficiency of the process and the temperatures of the heat produced are recognized to be the fluid critical temperature, the molecular complexity, the top cycle pressure and the amount of internal regeneration of heat. Two cycle configurations are examined: one featuring fluid compression after a regenerative preheating and one that also includes turbine expansion of a fraction of the high-pressure fluid in order to achieve a more effective regeneration. General diagrams giving the operating characteristics of a supercritical heat-pump cycle for any kind of fluid are reported. Some fluids are presented (SF 6, C 3F 8, C 2HF 5, c-C 4F 8), which exhibit a high level of thermal stability and are thermodynamically suitable for supercritical cycles: for each one a detailed performance chart is given. An example application in which a conventional high-temperature cycle is compared with two supercritical solutions is presented. The following conclusions summarize the findings of the thermodynamic analysis. (1) In supercritical cycles high heat-output temperatures are achievable with moderate compressor pressure ratios and with a comparatively simple cycle arrangement, while conventional cycles require a large pressure ratio and a complex cycle organization. Sub-atmospheric pressures, which may be required in conventional cycles, can be avoided. (2) As heat is available in supercritical cycles within a certain temperature range, applications implying the use of heat at variable temperature could benefit from the natural matching between temperature availability and process requirements. (3) The comparatively high pressures at which heat is produced in supercritical cycles could represent a drawback for small-capacity plants but are probably acceptable or even beneficial for large systems. (4) The internal regeneration of a sizeable amount of heat, which is requested in supercritical cycles, represents a definite cost item for this type of heat pump.

Calculation of the temperature of regenerative preheating of water in two-circuit atomic power plants

Calculation of the temperature of regenerative preheating of water in two-circuit atomic power plants

The temperature of regenerative pre-heating of water in an atomic power station with a water-cooled reactor

The temperature of regenerative pre-heating of water in an atomic power station with a water-cooled reactor