Optimization of a gas turbine in the methanol process,using the NLP model

Heat and power integration can reduce fuel usage, CO₂ and SO₂ emissions and, thereby, pollution. In the simultaneous heat and power integration approach and including additional production, the optimization problem is formulated using a simplified process superstructure. Nonlinear programming (NLP) contains equations which enable structural heat and power integration and parametric optimization. In the present work, the NLP model is formulated as an optimum energy target of process integration and electricity generation using a gas turbine with a separator. The reactor acts as a combustion chamber of the gas turbine plant, producing high temperature. The simultaneous NLP approach can account for capital cost, integration of combined heat and power, process modification, and additional production trade-offs accurately, and can thus yield a better solution. It gives better results than non-simultaneous methods. The NLP model does not guarantee a global cost optimum, but it does lead to good, perhaps near optimum designs.This approach is illustrated by an existing, complex methanol production process. The objective function generates a possible increase in annual profit of 1.7 MEUR/a.     

Boiling two-phase flow and efficiency of co- and counter-current microchannel heat exchangers with gas heating

To learn how to utilize the exhaust heat from a high-temperature gas product of a methanol reformer, the present study experimentally investigates the boiling two-phase flow in co- and counter-current microchannel heat exchangers (MCHE) with gas heating. Boiling two-phase flow patterns, two-phase flow instability, and efficiency are explored. The working fluid on the hot and cold sides are helium and liquid methanol, respectively. The silicon-based MCHE, which has dimensions of 20 mm × 20 mm, is designed with 18 parallel microchannels on both sides and is prepared using microfabrication processes. Four types of two-phase flow patterns – bubbly-elongated slug flow, annular flow, annular flow with liquid film breakup, and dryout are identified in both types of MCHE that are studied. A flow pattern map is then constructed on the plane of the methanol mass flux versus heat flux for both types of MCHE. In the counter-current MCHE, the efficiency increases significantly with an increase in the mass flux in both the single- and two-phase flow regions, while the effect of mass flux is insignificant in the co-current MCHE. In the two-phase flow region, the efficiency of both types of MCHEs gradually increases with an increase in the hot-side thermal power until the CHF is approached. The highest efficiency obtained in the present study is about 0.85 and 0.90 for the co- and counter-current MCHEs, respectively.     

Transport phenomena and performance of a plate methanol steam micro-reformer with serpentine flow field design

A numerical investigation of the transport phenomena and performance of a plate methanol steam micro-reformer with serpentine flow field as a function of wall temperature, fuel ratio and Reynolds number are presented. The fuel Reynolds number and H₂O/CH₃OH molar ratio (S/C) that influence the transport phenomena and methanol conversion are explored in detail. In addition, the effects of various wall temperatures on the plates that heat the channel are also investigated. The predictions show that conduction through the wall plays a significant effect on the temperature distribution and must be considered in the modeling. The predictions also indicate that a higher wall temperature enhances the chemical reaction rate which, in turn, significantly increases the methanol conversion. The methanol conversion is also improved by decreasing the Reynolds number or increasing the S/C molar ratio. When the serpentine flow field of the channel is heated either through top plate (Y = 1) or the bottom plate (Y = 0), we observe a higher degree of methanol conversion for the case with top plate heating. This is due to the stronger chemical reaction for the case with top plate heating.     

Regularities of flow and heat transfer at the surface of transversely finned tubes

A great number of experimental investigations allowing one to reveal the physical mechanism of processes responsible for their thermal and hydraulic performance are carried out in attempt to solve problems of updating constructions and methods of thermal design of heating surfaces of transversely finned tubes widespread in power engineering. Results of flow visualization and investigation of pressure fields and local heat transfer at the fin surface over the Reynolds number range Re = (1.0 ? 6.6) · 10⁴ are presented for the case of a wide variation of geometric characteristics of finned tubes and parameters of their arrangement in a bundle. Regularities substantially changing the existing concept of transfer processes in the interfin space and in the wake behind a finned tube are revealed. It is found that the flow behavior and the distribution of local heat transfer coefficients over the fin surface change significantly at the fin height-to-finned tube diameter h/d approximately equal to 0.4. The results obtained are generalized in the form of the patterns of flow and heat transfer at the finned tube surface, including seven characteristic regions and four types of flow separation.     

Magnesium oxide/water chemical heat pump to enhance energy utilization of a cogeneration system

A chemical heat pump using a magnesium oxide/water reaction system is expected to be applicable to cogeneration systems using gas engine, diesel engine, and fuel cells. The operability of the heat pump was examined experimentally under hydration operation pressures between 30 and 203 kPa. In the experiment, a reactant having high durability for repetitive operation was packed in a cylindrical reactor. The cycle of operation was repeated under various thermally driven operation conditions. The forward and reverse reactions were studied by measuring the reactor bed temperature distribution and the reacted fraction changes. The reactor bed stored heat at around 300–400 °C by the dehydration reaction and released heat at around 100–200 °C by the hydration reaction under the heat amplification mode operation. The practical possibility of the reactor bed was discussed based on the experimental results. The heat pump is expected to be applicable for load leveling in a cogeneration system by chemically storing surplus heat during low heat demand and supplying heat during peak demand. It was shown that the chemical heat pump would be able to improve the efficiency of energy utilization in cogeneration systems while also helping to reduce energy consumption and global carbon dioxide emissions.     

Experimental study of several types of ground heat exchanger using a steel pile foundation

An experimental study of several types of ground heat exchangers (GHEs) installed in a steel pile foundation, including double-tube, U-tube, and multi-tube GHEs, was carried out at Saga University. Water flows through the heat exchangers and exchanges heat to or from the ground. The performance of GHEs was investigated under actual operation in the cooling mode with flow rates of 2, 4, and 8 l/min. Temperatures of the ground and GHE tube wall were measured to find the temperature distributions according to the depth of the ground and depth of the GHE tube wall. The temperatures of the inlet and outlet of circulated water were also measured to calculate the heat exchange rate. The double-tube had the highest heat exchange rate, followed by the multi-tube and U-tube GHEs. For example, the average heat exchange rate of GHEs over 24 h of continuous operation with a flow rate of 4 l/min was 49.6 W/m for the double-tube, 34.8 W/m for the multi-tube, and 30.4 W/m for the U-tube. An increasing flow rate increased the heat exchange rate of the GHEs. The heat exchange rates increased significantly for flow rate increases from 2 to 4 l/min, but only slightly changed from 4 to 8 l/min.     

Integration of a cogeneration unit into a kraft pulping process

The integration of cogeneration with other measures that impact the power production capacity in a Canadian Kraft pulping mill is studied. Those measures are removal of pressure reduction valves, adjustment of the steam pressure level, biomass boiler capacity, and reduction in process energy demand. CADSIM Plus software is used to simulate the cogeneration plant. The dynamic behavior of the process during start-up and its effect on electricity generation are also considered. It is shown that by replacing the PRVs with turbines, 14.4 MW of power can be generated. Moreover, by implementing cogeneration units and process measures to recover 23% of internal energy, 44.5 MW of electricity can be generated in addition to shutting down the existing bunker oil boiler. Therefore, implementation of cogeneration in the pulp and paper industry is technically possible and it offers significant economic advantages. A cost analysis of the complete project gives a simple payback time of less than a year.     

Effects of water on the esterification of free fatty acids by acid catalysts

To maximize the production of biodiesel from soybean soapstock, the effects of water on the esterification of high-FFA (free fatty acid) oils were investigated. Oleic acid and high acid acid oil (HAAO) were esterified by reaction with methanol in the presence of Amberlyst-15 as a heterogeneous catalyst or sulfuric acid as a homogeneous catalyst. The yield of fatty acid methyl ester (FAME) was studied at oil to methanol molar ratios of 1:3 and 1:6 and reaction temperatures of 60 and 80 °C. The rate of esterification of oleic acid significantly decreased as the initial water content increased to 20% of the oil. The activity of Amberlyst-15 decreased more rapidly than that of sulfuric acid, due to the direct poisoning of acid sites by water. Esterification using sulfuric acid was not affected by water until there was a 5% water addition at a 1:6 molar ratio of oil to methanol. FAME content of HAAO prepared from soapstock rapidly increased for the first 30 min of esterification. Following the 30-min mark, the rate of FAME production decreased significantly due to the accumulation of water. When methanol and Amberlyst-15 were removed from the HAAO after 30 min of esterification and fresh methanol and a catalyst were added, the time required to reach 85% FAME content was reduced from 6 h to 1.8 h.     

Entropy generation of vapor condensation in the presence of a non-condensable gas in a shell and tube condenser

This article investigates the entropy production of condensation of a vapor in the presence of a non-condensable gas in a counter-current baffled shell and one-pass tube condenser. The non-dimensional entropy number is derived with respect to heat exchange between the bulk fluid and condensate, as well as heat exchange between the condensate and coolant. Numerical results show that heat transfer from the condensate to the coolant has a dominant role in generating entropy. For example, at an air mass flow rate of 330 kg/h, 93.4% of the total entropy generation is due to this source. The resultant profiles during the condensation process indicate that a higher air mass flow rate leads to a lower rate of entropy production. For example, as the air mass flow rate increases from 330 kg/h to 660 kg/h and 990 kg/h, the total entropy generation decreases from 976 J/s K to 904 and 857.2 J/s K, respectively. By introducing a new parameter called the condensation effectiveness, a correlation is also developed for predictions of the entropy number, and an illustrative example is presented.     

Gasification of hazelnut shells in a downdraft gasifier

The potential offered by biomass to reduce greenhouse gas production is now being more widely recognised. The energy in biomass may be realised either by direct combustion use, or by upgrading into more valuable and useable products such as gas, fuel oil and higher value products for utilisation in the chemical industry or for clean power generation. Up till now, gasification work has concentrated on woody biomass but recently sources of other biomass with large energy production potential have been identified, namely hazelnut shells. Therefore, a pilot scale downdraft gasifier is used to investigate gasification potential of hazelnut shells. A full mass balance is reported including the tar production rate as well as the composition of the produced gas as a function of feed rate. Additionally, the effect of feed rate on the CV/composition of the product gas and the associated variations of gasifier zone temperatures are determined with temperatures recorded throughout the main zones of the gasifier and also at the gasifier outlet and gas cleaning zones. Pressure drops are also measured across the gasifier and gas cleaning system because the produced gas may be used in conjunction with a power production engine when it is important to have low pressure drop in the system. The quality of the product gas is found to be dependent on the smooth flow of the fuel and the uniformity of the pyrolysis, and so the difficulties, encountered during the experiments are detailed. The optimum operation of the gasifier is found to be between 1.44 and 1.47 N m³/kg of air fuel ratios at the values of 4.06 and 4.48 kg/h of wet feed rate which produces the producer gas with a good GCV of about 5 MJ/m³ at a volumetric flow of 8–9 N m³/h product gas. It was concluded that hazelnut shells could be easily gasified in a downdraft gasifier to produce good quality gas with minimum polluting by-products. It is suggested that, in view of ease of operation, small-scale gasifiers can make an important contribution to the economy of rural areas where the residues of nuts are abundant. It is also suggested that gasification of shell waste products is a clean alternative to fossil fuels and the product gas can be directly used in internal gas combustion engines, thus warranting further investment/encouragement by authorities to exploit this valuable resource.     

A plate-type reactor coated with zirconia-sol and catalyst mixture for methanol steam-reforming

A plate-type reactor with 10 channels is designed for methanol steam-reforming and its performance is investigated in the temperature range 210–290 °C. A catalyst coated with zirconia-sol solution in the channels of the reactor exhibits a good adherence with the substrate that is maintained even after reaction including fast feed flow rates at high temperature. Five plate-type reactors are stacked in order to test their performance for methanol steam-reforming. At 270 °C, hydrogen at 3.1 l h⁻¹ is obtained at a feed flow rate of 2.0 g h⁻¹, which corresponds to results for a conventional packed-bed reactor under various reaction conditions.     

Present and future trends in pellet markets,raw materials,and supply logistics in Sweden and Finland

Wood pellets have become an important fuel in heat and power production, and pellet markets are currently undergoing rapid development. In this paper, the pellet markets, raw materials and supply structures are analyzed for Sweden and Finland, based on a database of the current location and production capacity of the pellet producers, complemented with existing reports and literature. In Sweden, a total of 94 pellet plants/producers were identified, producing 1.4 million tonnes of pellets, while the domestic consumption was 1.7 million tonnes, and about 400,000 t of pellets were imported to fulfil the demand in 2007. In Finland, 24 pellet plants/producers were identified and the production was around 330,000 t while the domestic consumption was 117,000 t in 2007. In Finland, pellet market has been long time export oriented, whereas domestic consumption has been growing mainly in the small scale consumer sector, estimated 15,000 households had pellet heating systems in 2008. In the future, the increasing number of pellet users will require a reliable delivery network and good equipment for bulk pellet deliveries. Provision of new raw materials and ensuring the good quality of pellets through the whole production, delivery and handling chain will be fundamental in order to increase the use of pellets and sustain the ability to compete with other fuels.     

Hybrid sulfur flowsheets using PEM electrolysis and a bayonet decomposition reactor

A conceptual design is presented for a hybrid sulfur process for the production of hydrogen using a high-temperature nuclear heat source to split water. The process combines proton exchange membrane-based SO₂-depolarized electrolyzer technology being developed at Savannah River National Laboratory with silicon carbide bayonet decomposition reactor technology being developed at Sandia National Laboratories. Both are part of the US DOE Nuclear Hydrogen Initiative. The flowsheet otherwise uses only proven chemical process components. Electrolyzer product is concentrated from 50 wt% sulfuric acid to 75 wt% via recuperative vacuum distillation. Pinch analysis is used to predict the high-temperature heat requirement for sulfuric acid decomposition. An Aspen Plus? model of the flowsheet indicates 340.3 kJ high-temperature heat, 75.5 kJ low-temperature heat, 1.31 kJ low-pressure steam, and 120.9 kJ electric power are consumed per mole of H₂ product, giving an LHV efficiency of 35.3% (41.7% HHV efficiency) if electric power is available at a conversion efficiency of 45%.     

Analysis for heat transfer enhancement of helical and electrical heating tube heat exchangers in vacuum freeze-drying plant

This paper investigates the heat transfer rate of the combined cooling-and-heating heat exchanger by using computational fluid dynamics (CFD) method. Several factors, such as additional baffles and heat transfer areas, are also discussed in order to improve the efficiency of heat exchanger in the vacuum freeze-drying system. The simulated result indicated that, for addition electrical heating tube, the heat transfer rate of the heat exchanger increased with the increasing length of the electrical heating tube. The increasing rates of secondary and primary drying stages were 2.774 and 2.986 W/mm, respectively. For additional vertical baffle, the variation of the heat transfer rate with respect to vertical baffle length was in the U-shape format. The minimum heat transfer rates of secondary drying, primary drying and freezing stages were 716.79 W and − 195.17 W and − 670.71 W, respectively. For additional W-shape vertical baffles, the heat transfer rate of this heat exchanger was maximum among these four designs. For the three stages of heat exchangers with these four designs, the shell side Nusselt number had the inverse linear relationship with the Reynolds number.     

Experimental study on flame height and temperature profile of buoyant window spill plume from an under-ventilated compartment fire

Fire experiments were carried out in a scale model, consisting of an 0.8 m cubic fire compartment with six window like geometries and an attached 3 m (wide) × 5 m (high) façade wall. A propane porous gas burner with controlled fuel supply rate was the fire source. Gas temperature profiles were measured inside the compartment and near the façade wall. The outside spill flame heights were recorded by a CCD Digital camera. Temperature and flame heights are correlated with heat release rate and the window geometry using physically non-dimensional analysis. The steady gas temperatures inside the compartment are determined by an overall energy balance between the heat release rate inside the compartment and the wall conduction and opening radiation heat losses using an effective overall heat loss coefficient. Flame heights on the façade are non-dimensionally correlated by the excess fuel heat release rate outside the enclosure and a characteristic length scale for the window. These results agree with previous results in the literature. Vertical gas temperatures near the façade wall outside the enclosure are non-dimensionally correlated with the total convective heat flow rate above the flames and the same characteristic window length scale as the flame height, with the additional necessary determination of a virtual origin of the convective flow above the flame. These results and correlations are new and a significant improvement over previous results in the literature.     

Investigation of natural convection induced outer side heat transfer rate of coiled-tube heat exchangers

Natural convection induced heat transfer has been studied over the outer surface of helically coiled-tube heat exchangers. Several different geometrical configurations (curvature ratio δ ε [0.035, 0.082]) and a wide range of flow parameters (60 <= T_tank <= 90, T_in = 19 and 60 <= T_in <= 90, T_tank = 20, 4000 <= Re <= 45000) have been examined to broaden the validity of the results gained from this research. A fluid-to-fluid boundary condition has been applied in the numerical calculations to create the most realistic flow configurations. Validity of the numerical calculations has been tested by experiments available in the open literature. Calculated results of the inner side heat transfer rate have also been compared to existing empirical formulas and experimental results to test the validity of the numerical computation in an independent way from the outer side validation of common helical tube heat exchangers. Water has been chosen to the working fluid inside and outside of the coiled tube (3 < Pr < 7). Outer side heat transfer rate along the helical tube axis has been investigated to get information about the performance of the heat transport process at different location of the helical tube. It was found that the outer side heat transfer rate is slightly dependent on the inner flow rate of any helical tube in case of increasing temperature differences between the tank working fluid temperature and the coil inlet temperature. A stable thermal boundary layer has been found along the axial direction of the tube.In addition to this the qualitative behavior of the peripherally averaged Nusselt number versus the axial location along the helical tube function is strongly dependent on the direction of the heat flow (from the tube to the storage tank and the reversed direction). Inner side heat transfer rate of helical coils have also been investigated in case of fluid-to-fluid boundary conditions and the calculation results have been compared with different prediction formulas published in the last couples of decades.     

Acid-catalyzed production of biodiesel from waste frying oil

The reaction kinetics of acid-catalyzed transesterification of waste frying oil in excess methanol to form fatty acid methyl esters (FAME), for possible use as biodiesel, was studied. Rate of mixing, feed composition (molar ratio oil:methanol:acid) and temperature were independent variables. There was no significant difference in the yield of FAME when the rate of mixing was in the turbulent range 100 to 600 rpm. The oil:methanol:acid molar ratios and the temperature were the most significant factors affecting the yield of FAME. At 70 °C with oil:methanol:acid molar ratios of 1:245:3.8, and at 80 °C with oil:methanol:acid molar ratios in the range 1:74:1.9–1:245:3.8, the transesterification was essentially a pseudo-first-order reaction as a result of the large excess of methanol which drove the reaction to completion (99±1% at 4 h). In the presence of the large excess of methanol, free fatty acids present in the waste oil were very rapidly converted to methyl esters in the first few minutes under the above conditions. Little or no monoglycerides were detected during the course of the reaction, and diglycerides present in the initial waste oil were rapidly converted to FAME.     

Experimental analysis of flow and heat transfer in a miniature porous heat sink for high heat flux application

A novel miniature porous heat sink system was presented for dissipating high heat fluxes of electronic device, and its operational principle and characteristics were analyzed. The flow and heat transfer of miniature porous heat sink was experimentally investigated at high heat fluxes. It was observed that the heat load of up to 280 W (heat flux of 140 W/cm²) was removed by the heat sink with the coolant pressure drop of about 34 kPa across the heat sink system and the heater junction temperature of 62.9 °C at the coolant flow rate of 6.2 cm³/s. Nu number of heat sink increased with the increase of Re number, and maximum value of 323 for Nu was achieved at highest Re of 518. The overall heat transfer coefficient of heat sink increased with the increase of coolant flow rate and heat load, and the maximal heat transfer coefficient was 36.8 kW(m² °C)^?1 in the experiment. The minimum value of 0.16 °C/W for the whole thermal resistance of heat sink was achieved at flow rate of 6.2 cm³/s, and increasing coolant flow rate and heat fluxes could lead to the decrease in thermal resistance. The micro heat sink has good performance for electronics cooling at high heat fluxes, and it can improve the reliability and lifetime of electronic device.     

Effects of heat flux,vapour quality,channel hydraulic diameter on flow boiling heat transfer in variable aspect ratio micro-channels using transparent heating

Experiments on flow boiling heat transfer in high aspect ratio micro-channels with FC-72 were carried out. Three channels with different hydraulic diameters (571, 762 and 1454 μm) and aspect ratios (20, 20 and 10) were selected. The tested mass fluxes were 11.2, 22.4 and 44.8 kg m^?2 s^?1 and heat fluxes ranging from 0–18.6 kW m^?2. In the present study, boiling curves with obvious temperature overshoots are presented. Average heat transfer coefficient and local heat transfer coefficient along stream-wise direction are measured as a function of heat flux and vapour quality respectively. Slug-annular flow and annular flow are the main flow regimes. Convective boiling is found to be the dominant heat transfer mechanism. Local heat transfer coefficient increases with decreasing hydraulic diameter. Moreover, the effect of hydraulic diameter is more significant when mass flux is higher. The unique channel geometry is considered as the decisive reason of the flow regimes as well as heat transfer mechanisms.     

Exergoeconomic analysis of gas turbine cogeneration systems

A thermodynamic for the effect of the annualized cost of a component on the production cost in 1 000 kW gas-turbine cogeneration system was studied by utilizing the generalized exergy balance and cost-balance equations developed previously. Comparison between typical exergy-costing methodologies were also made by solving a predefined cogeneration system, CGAM problem. It was successful to identity the component which affects the unit cost of system's products decisively. It has been found that the cost of products are crucially dependent on the change in the annualized cost of the component whose primary product is the same as the system's product. On the other hand, the change in the weighted average cost of the product is proportional to the change in the annualized cost of the total system.