Heat Recovery Section Research Articles

Simulation of a waste incineration process with flue-gas cleaning and heat recovery sections using Aspen Plus

In the present paper, the modeling of a dual-purpose plant for the production of electrical and thermal energy from the heat treatment of solid wastes is presented. Particularly, the process has been modeled by using the Aspen Plus Shell, with the aim of performing a study about the applicability of this software in the simulation of a solid waste incineration process, which involves complex gas–solid reactions where the solids are referred to as “non-conventional”. The model is developed to analyze and quantify the expected benefits associated with refuse derived fuel (RDF) thermal utilization; thus attention is focused on the performance of the energy recovery section.

Experimental study on multi-layered type of gas-to-gas heat exchanger using porous media

Based on an effective energy conversion method between flowing gas enthalpy and thermal radiation, a multi-layered type of gas-to-gas heat exchanger using porous media has been proposed. A series of experiments have been conducted for the inlet temperature of high temperature gas 300–700 °C, the optical thickness of porous media 0–15.4, the number of layers 2–5 and two types of walls (bare or finned) placed in the system. As a result, a heat recovery section is shown to play an important role in lowering an outer wall temperature of the system and at the same time in increasing the total heat recovery rate H tot, N . In addition, it is clarified that the optical thickness of about 8 is enough to obtain sufficient H tot, N , and the finned walls are quite effective to promote H tot, N under the present experimental conditions.

03/01688 Coal gasifier preventing inorganic compound condensation in heat or char recovery section: Yamada, M. et al. Jpn. Kokai Tokkyo Koho JP 2003 20,486 (Cl. C10J3/00), 24 Jan 2003, Appl. 2001/205,644. (In Japanese)

03/01688 Coal gasifier preventing inorganic compound condensation in heat or char recovery section: Yamada, M. et al. Jpn. Kokai Tokkyo Koho JP 2003 20,486 (Cl. C10J3/00), 24 Jan 2003, Appl. 2001/205,644. (In Japanese)

Analysis of multiple effect distillation Part II. Dynamic model

In this study, the MED unit is divided into two sections: heat recovery section and heat rejection section. The heat recovery section consists of a series of effects, while the heat rejection section consists of one effect only (condenser). The MED system contains the evaporators, feed water preheaters and the flashing tanks (boxes). The physical model of effect number i th of MED unit is considered. The physical model can be divided into five compartments such as brine pool, vapor space, condensate tube bundle, feed water preheater and flash tank. The mass, salt and energy balance equations for each previous compartment have been solved dynamically taking into consideration the effect of each one on the other. Dynamic equations in each of the last five compartments mentioned are formulated mathematically for the whole MED system. All effects have identical dynamic equations, except the first evaporator (effect), last evaporator (condenser), and the first flashing tank are formulated mathematically stand-alone. To obtain a proper dynamic model solution, without simplification and complicated approaches, some assumptions have been considered and will be mentioned in the final manuscript. A disturbance technique for the choice parameters has been done to perform the dynamic model program and study the reaction of that disturbance on the behavior of the remaining parameters studied.

A Review of Study on Thermal Energy Transport System by Synthesis and Decomposition Reactions of Methanol

The study on thermal energy transport system by synthesis and decomposition reactions of methanol was reviewed. To promote energy conservation and global environment protection, a two-step liquid-phase methanol synthesis process, which starts with carbonylation of methanol to methyl formate, then followed by the hydrogenolysis of the formate, was studied to recover wasted or unused discharged heat from industrial sources for the thermal energy demands of residential and commercial areas by chemical reactions. The research and development of the system were focused on the following three points. ( 1 ) Development of low-temperature decomposition and synthetic catalysts, ( 2 ) Development of liquid phase reactor (heat exchanger accompanying chemical reaction), ( 3 ) Simulation of the energy transport efficiency of entire system which contains heat recovery and supply sections. As the result of the development of catalyst, promising catalysts which agree with the development purposes for the methyl formate decomposition reaction and the synthetic reaction are being developed though some studies remain for the methanol decomposition and synthetic reactions. In the fundamental development of liquid phase reactor, the solubilities of CO and H 2 gases in methanol and methyl formate were measured by the method of total pressure decrease due to absorption under pressures up to 1 500 kPa and temperatures up to 140°C. The diffusivity of CO gas in methanol was determined by measuring the diameter and solution time of single CO bubbles in methanol. The chemical reaction rate of methanol synthesis by hydrogenolysis of methyl formate was measured using a plate-type of Raney copper catalyst in a reactor with rectangular channel and in an autoclave reactor. The reaction characteristics were investigated by carrying out the experiments at various temperatures, flow rates and at various catalyst development conditions. We focused on the effect of Raney copper catalyst thickness on the liquid-phase chemical reaction by varying the development time of the catalyst. Investigation results of the catalyst such as surface area, pore radius, lattice size, and photographs of scanning electron microscope (SEM) were also given. In the simulation of energy transport efficiency of this system, by simulating the energy transfer system using two-step liquid phase methanol decomposition and synthetic reactions, and comparing with the technology so far, it can be expected that an innovative energy transfer system is possible to realize.

A Neural Network Simulator of a Gas Turbine With a Waste Heat Recovery Section

The objective of the paper is to assess the feasibility of the neural network (NN) approach in power plant process evaluations. A “feed-forward” technique with a back propagation algorithm was applied to a gas turbine equipped with waste heat boiler and water heater. Data from physical or empirical simulators of plant components were used to train such a NN model. Results obtained using a conventional computing technique are compared with those of the direct method based on a NN approach. The NN simulator was able to perform calculations in a really short computing time with a high degree of accuracy, predicting various steady-state operating conditions on the basis of inputs that can be easily obtained with existing plant instrumentation. The optimization of NN parameters like number of hidden neurons, training sample size, and learning rate is discussed in the paper.

Multistage flash desalination combined with thermal vapor compression

A novel system is proposed to increase the performance of the multistage flash desalination process (MSF) by combination with thermal vapor compression (TVC). The proposed system integrates the vapor compression unit within the conventional MSF brine circulation configuration without variations in the process layout. Two schemes are evaluated, which includes vapor entrainment and compression from the heat recovery or rejection sections. These schemes may call for use of one or two jet ejectors depending on the required compression range. Performance evaluation for the proposed schemes is made as a function of the top brine temperature and location of vapor entrainment. Results show that the increase in thermal performance ratio of the proposed system over the conventional MSF varies between 6 and 16%. Additional power savings are realized as a result of 62–74% reduction in the specific flow rate of cooling water to the system. Use of high pressure steam results in 60% size reduction in the diameter of the steam piping system. Use of the steam jet ejector, eliminates the control loops and process units for throttling and desuperheating, which are found in conventional MSF. Vapor entrainment and compression from the stages of the heat recovery section gives higher thermal performance ratio and lower specific heat transfer area than for vapor entrainment from the heat rejection stages. However, the main advantage for vapor entrainment and compression from the heat rejection stages is that the specific flow rate of cooling water is lower by 40%. Gains and features of the proposed vapor compression modes would reduce the unit product cost as a result of reduction in the capital and operating costs of the process.

Model reduction and robust control of multi-stage flash (MSF) desalination plants

An orthogonal collocation method is used for the reduction of a large nonlinear model of a multi-stage flash (MSF) desalination plant. The real plant located in Saudi Arabia consists of 19 stages in the heat recovery section and three in the heat rejection section. It is shown that three collocation points, i.e., two for the heat recovery section and one for the heat rejection section, are sufficient for a good representation of the full-order model for both steady-state and dynamic behavior. The reduced model is then used for a robust controller design of the plant using a constrained nonlinear model predictive control (NLMPC) strategy. Numerical simulations show that the controlled system obtained when the reduced model is used for output prediction yields the same performances as with the full-order model but with a considerable reduction in the computational time and a much easier tuning of the controller.

The non-equilibrium factor and the flashing evaporation rate inside the flash chamber of a multi-stage flash desalination plant

A study was undertaken to measure the non-equilibrium factor and to correlate the flashing evaporation rate inside the flash chamber of a multi-stage flash (MSF) desalination plant. A computer code was developed to quantitatively simulate the MSF desalination plant operation and solve the mass, heat and salt balance equations. The simulator was tested against an MSF pilot plant with a four-stage heat recovery section and a two-stage heat rejection section, and then used to technically evaluate the flash chamber performance. For a constant top brine temperature of 112°C, the results indicated that (1) the non-equilibrium factor (1-β) varies between 0.24 to 0.66 (low values of flash chamber effectiveness, β). In order to reach thermodynamic equilibrium, the flashing evaporation process should be enhanced through increasing the brine superheat, flashing surface area, number of active nucleation sites, and brine residence time inside the flash chamber; (2) the average flashing heat flux ranges from 100 to 200 kW/m 2 and increases with the brine superheat and the stage pressure. Similar to the surface nucleate boiling, the flashing heat flux could be correlated as: Q″ = 0.055( T b( av) −T sat ) 3.

95/05870 Coal gasifier with heat recovery section

Integrating gasifiers with gas turbines, aeroderivative gas turbines in particular, makes it possible to achieve high efficiencies and low unit capital costs in modest-scale biomass power generating facilities. Electricity produced with biomass-integrated gasifier/gas turbine (BIG/GT) power systems would be competitive with electricity produced from coal and nuclear energy under a wide range of circumstances. Biomass also offers major environmental benefits. Initial applications will be with biomass residues generated in agro- and forest-product industries. Eventually, biomass grown for energy purposes on dedicated energy farms will also be used to fuel these gas turbine systems. Continuing improvements in jet engine and biomass gasification technologies will lead to further gains in the performance of BIG/GT systems over the next couple of decades.

Performance test of a new antiscalant “AQUAKREEN KC-550” under high temperature conditions at the MSF desalination plant in Dubai

Polycarboxyl type antiscalants in general have a tendency to become less effective in the presence of multi-valent metal ions such as Ca ++ and Mg ++ in sea water. However, Kao's new antiscalant “AQUAKREEN KC-550” improved by the copolymerization technology, has much higher stability against such multi-valance ions. AQUAKREEN KC-550 was tested by Dubai Electricity Company of the unit No.3 desalination plant at Jebel Ali “D” station under the dosing rate of 2 ppm at the brine top temperature of 105°C for a period of 5 months, with caution steps taken to set the optimum dosing rate beforehand. Through this performance test, it was proved that “AQUAKREEN KC-550” could successfully keep very stable all operation parameters such as the Heat Transfer Coefficients of both the brine heater and the heat recovery section and the Gained Output Ratio.

Steam-Injected Gas Turbine Integrated With a Self-Production Demineralized Water Thermal Plant

A simple steam-injected gas turbine cycle equipped with an exhaust heat recovery section is analyzed. The heat recovery section consists of a waste heat boiler, which produces the steam to be injected into the combustion chamber, and a self-production demineralized water plant based on a distillation process. This plant supplies the pure water needed in the mixed steam-gas cycle. Desalination plant requirements are investigated and heat consumption for producing distilled water is given. Overall steam-gas turbine cycle performance and feasibility of desalting plants are investigated in a firing temperature range from 1000.°C to 1400.°C for various compressor pressure and steam-to-air injection ratios. An example is reported.

Mesure en ligne de l'encrassement et du nettoyage d'un sterilisateur UHT industriel

An on-line fouling sensor for industrial heat exchangers used in food processing has been designed. Its principle is based on the evaluation of disturbances in the hydrodynamic functioning of the heat exchanger due to fouling. It was tested on an industrial plate heat exchanger used for UHT milk sterilization (10 m 3 h −1) to indicate the degree of fouling (α) in the heat-recovery section (milk temperature increasing from 80 to 120°C) and in the heating section (milk temperature increasing from 120 to 140°C). The final values of α can reach about 0·5 for each section. Furthermore, quality has a not insignificant effect on the kinetics of fouling and degree of deposition. The sensor is also able to measure fouling during cleaning processes. Thus, the cleanliness of the sterilizer can be evaluated. The sensor opens the way for the complete control and optimization of cleaning processes.

Better M.S.F. plant performance by avoiding tube fouling and debris

Despite the use of chemical scale inhibitors, fouled layers still form on the tubes in the brine heater and heat recovery sections of M.S.F. plants, necessitating the use of mechanical cleaning. Operating experience with GEA-EST On-line Tube Cleaning Systems in the Gulf Region is presented. The reasons for developing the batch system are outlined. The main features of the system described are reliability, low maintenance and ease of operation. Good ball distribution and avoidance of ball damage are essential requirements, and are fulfilled by this design. The benefits to be gained by the installation of a GEA-EST ball cleaning system in the heat rejection section include not only improved heat transfer but also better corrosion resistance. The need for some form of secondary screening close to the heat rejection section or make-up inlet is emphasized.

Energetic aspects of the fouling of MSF desalination plants with and without the use of on load ball cleaning system

Multi-stage flash (MSF) desalination plants are designed with specific permissible fouling factors. When these conditions are met, the performance is said to “meet design”. With single- purpose desalinators, fouling of the brine heater can be compensated for by increasing the steam pressure without substantial increase of heat consumption and within the limits of the boiler pressure. With dual-purpose desalinators, the brine heater pressure will influence the efficiency of the turbine process. Fouling of the heat recovery section increases the heat consumption of the MSF process. The distillate production can be maintained within the limits of the boiler. Typical “design fouling factors” have been compiled from literature. The influence of fouling factor on specific heat consumption has been calculated for typical MSF design conceptions, as well as the increase of water costs per m 3 with different fuel prices. The costs of various scale prevention methods have been evaluated. The effectiveness of such countermeasures can be quantified by plant experience. This analysis of cost/return gives a basis for a correct economic comparison.

A control system for multi-stage flash desalination plants

A system of simple analog control loops has been investigated experimentally in a 6-stage flashing test unit, which is aimed to automate the plant operation and to improve the distillation process within any required operating condition. The control circuit includes the control of liquid levels and temperatures in the first and last flashing chamber, adjusting automatically the amount of steam to the brine heater, and the brine flow rates in both the heat rejection and the heat recovery section. Using this system, the load can be changed more easily and quickly than by manual operation, which is an important factor for dual purpose plant coupling. Experiments have been carried out and simulated with a modified. form of a digital computer code published, by ORNL (ref. 3). Calculated and experimental results have been found to agree with one another very closely. The computer program was also applied to a MSF plant design with a higher number of stages. One of the main results is that, by decreasing the load, interstage blow-through can occur in the middle stages of the plant, even if the liquid levels in the first and in the last stage are kept constant. It is shown that the presence of weirs in the flashing chambers reduces this tendency.

The use of titanium tubes in MSF desalination plants

The use of titanium tubes in MSF desalination plants can eliminate all chances of tube failure throughout the expected life of the plant. Service experience over many years has demonstrated the complete absence of tube failures due to any corrosion or erosion mechanism in power station condensers. This demonstrates completely the suitability of titanium for the heat rejection stage of an MSF plant. This complete freedom from tube failures can also be expected in the higher temperatures and brine concentrations found in the heat recovery and brine heater sections of an MSF plant. To achieve the reliability required attention has to be given to the choice of compatible materials and tube fixing techniques. The mechanisms of crevice corrosion, of galvanic corrosion and of titanium hydriding will be discussed and choice of materials and techniques will be described which will avoid these problems. Titanium's total resistance to erosion can also be used to give a significant improvement in the heat transfer efficiency. This can be simply achieved by increasing the water velocity but can be very much further increased by the use of advanced geometry titanium tube. The choice of appropriate design of advanced geometry titanium tube will be presented together with the effects on the heat transfer coefficients and the pressure drop along the tube.

多段フラッシュ海水淡水化装置の伝熱管材料に関する研究

The application of ferrous materials to heat exchanger tubes in an MSF desalination plant have attracted serious attention, because of their low price and availability. In this national project, the ferrous materials mainly examined were low alloy steels, but stainless steels and coated steels were also tested. The test results of these ferrous materials were as follows. (1) Low alloy steels: In the loop test 17 kinds of low alloy steels were tested, the majority of which were low chromium steels. The corrosion rates of these steels were reduced with increasing content of chromium, but above 5% of chromium the tendency of local corrosion increased. Under the brine condition corresponding to a heat recovery section, 2Cr to 3Cr steels exhibited good corrosion resistance. In the field test, 2Cr to 3Cr steel tubes selected by the loop test were mounted in each stage of the heat recovery section. Contrary to expectation, in the field test the corrosion rates increased more than several times over those in the loop test. From the results of these tests 3Cr-1Al, 3Cr-1Ni and 2Cr-0.1Mo-1.2Mn-0.26Cu steels were selected. The increase of the corrosion rates of these steel tubes in the field test was inferred as follows: deposition of iron rich sludge from circulating brine in the steel tubes (produced by the corrosion of steel shells in contact with the brine) might have an accelerating effect on corrosion of the tubes by the Schikorr reaction. This suggested that continuous removal of iron rich sludge from the steel tubes by sponge-ball cleaning might improve the corrosion resistance of the steel tubes. (2) Stainless steels: In the loop test stainless steels indicated more or less the tendency of local corrosion, especially at the crevice formed by Teflon holders. In the field test, test tubes of stainless steels selected from the loop test were placed in the sections of the brine heater and the heat rejection (where corrosion troubles of copper alloy tubes have been liable to occur). As the results, several stainless steels superior to 316 steel were found. These were three 25 chromium dual phase steels, two high nickel austenite steels and one 25 chromium ferrite steel. However some open type micro pits were observed under sludge in all of these high grade stainless steel tubes. This pitting-like local corrosion may be a form of crevice corrosion caused by the deposition of sludge. Therefore, the continuous removal of sludge by sponge-ball cleaning or the development of more resistant stainless steels is desired. (3) Coated steels: In the loop and the field test some metallic coatings (chromized, aluminized, etc.) and some organic coatings (phenol resin or epoxy resin) were tested. The defect in chromized steel was pitting corrosion originated in pinholes, and that in aluminized steel was the dissolution of aluminum layer which was accelerated by the increased temperature of sea water. Corrosion resistance of the organic coatings was excellent, but because of the extremely low thermal conductivity, coating thickness and the adherence of sludge, the overall heat transfer coefficients were very small. Because of these disadvantages, it seems that the use of coated steel tubes is still not practical.

Deodorizing system modification for heat recovery and steam refining of palm oil

AbstractWith continuous deodorizers of the double shell type most of the steam normally used to preheat the feedstock in the deaerating section can be saved by a modification‐the essential feature of which is the addition of a heat recovery section location between the final deodorizing section and the cooling section, by means of which heat is transferred from the hot deodorized oil to the feedstock. Consistent with the principles of the original design, no pumping or piping of hot oil outside the deodorizer is required. Continuous deodorizers of the stripping tray type can be modified for “steam refining” or “stripping” of high free fatty acid palm oil to reduce the free fatty acid palm oil to reduce the free fatty acids to 0.03% max. This is accomplished by means of additional trays in the stripping sections of the deodorizer. The capacity, sparge steam temperature, vacuum and retention time remain the same as with normal deodorization.