Developments in the engineering of refrigeration installations for cooling mines

The need to reduce the electrical energy consumption associated with the cooling of mines has recieved considerable attention in recent years. Various methods for reducing the amount of cooling water circulated underground in mines has also been looked at. These requirements have led to several developments such as cooling of the ventilation air on surface, the use of energy recovery devices, refrigeration machines for producing water close to 0°C and currently consideration is being given to installing ice making machines on the surface. These developments and their field of application are analysed and discussed.     

Assessment criteria for solar cooling systemsCritères pour l'évaluation des systèmes frigorifiques solaires

Solar cooling systems should be able simultaneously to generate refrigeration and save conventional energy. An assessment of the potential of various cooling systems as refrigerators and energy savers is presented in the paper. For this purpose, a solar cooling system has been considered as a combination of an energy conversion and a refrigeration subsystem. Overall efficiencies of the various solar cooling systems are defined for direct quantitative comparison of different systems.     

Performance results of solar absorption cooling installationRésultats de la performance d'une installation frigorifique solaire à absorption

This paper describes a solar absorption cooling system and its performance for an office building having an occupancy of 7 h per day. The absorption system of 40 RT cooling capacity (installed) uses 300 m² of flat plate collector area and an oil-fired supplementary thermal energy source. The system produces > 10 000 kWh cooling per month. Considering the parasitic electric energy needs and the electrical energy equivalent of make-up water consumed in the energy rejection subsystem, the solar cooling installation saves 25–40% per day of electrical energy when compared to an equivalent cooling capacity conventional cooling system.     

Machine frigorifique à absorption (eau-ammoniac) fonctionnant avec des capteurs plans sur le site de Rabat

Two-stage absorption refrigerating machines driven by solar energy have been studied for cooling applications in Morocco. A simulation program allowing the calculation of the efficiency, cooling effect and dynamic behaviour of a complete installation, including solar collectors, absorption machines and heat storage has been established. This takes into account the real efficiency of each element of the installation and a parametric study of various machine configurations has been made. The two-stage absorption machine working with the fluid pair NH₃---H₂O, with two desorbers in parallel but without a rectifying column, has been shown to be the best choice for use with flat plate solar collectors. The optimum working conditions of the machine have been determined using the hourly radiation and climatic data for the city of Rabat, Morocco. In order to ensure the continuous production of cold, the behaviour of an installation to which energy storage on the warm and cold sides have been added has been determined.     

Economic optimization of refrigeration plantsOptimisation économique des installations frigorifiques

The economic optimization of refrigeration plants is discussed. In the optimization procedure it is often necessary to compare several different optimized concepts of the refrigeration system, eg screw compressors versus reciprocating compressors. Optimization procedures are discussed and the optimum values found by the computer program are compared with results calculated with Bäckström equations. Estimation of future changes in the cost of electricity and water, and rates of interest and inflation have to be included in the optimization procedure. Even so, it may be difficult to persuade the purchaser to afford the optimum plant.     

Simulation d'une machine frigorifique à absorption fonctionnant avec des mélanges d'alcanes

We propose in this article an absorption chiller operating with binary alkane mixtures as an alternative to compression machines. It is an installation using low-level energy at a temperature below 150 °C (waste heat or solar energy) and operating with environmentally friendly fluids. Ten mixtures are considered and compared with two cooling mediums of the condenser and the absorber: the ambient air at 35 °C and the water at 25 °C. For an air-cooled chiller, the COP reaches 0.37 for the n-butane/octane system. This value remains 27% lower than that of an ammonia/water installation operating under the same conditions. For a water-cooling chiller, the n-butane/octane and propane/octane systems give a COP of about 0.63, which is comparable to that of the ammonia/water system. When n-butane is used as refrigerant, the machine works at a pressure under 5 bars, which is an advantage compared with machines working with ammonia/water mixtures.     

Thermal energy reservoir capacities for solar absorption cooling systemsCapacité des accumulateurs d'énergie thermique pour les systèmes frigorifiques à absorption solaires

It is essential to incorporate both hot and cold energy storage for a solar absorption cooling system in order to maximize the saving of conventional electrical power. The paper correlates the thermal energy storage requirements with the daily cooling demand pattern of a building. The other parameters which affect the choice of the two storage volumes are the effective sunshine hours, the chiller cooling capacity, its daily operation period and the two storage temperature differentials. The results have been obtained in a generalized manner and applied to an actual building in Kuwait.     

Etude des facteurs d'intensification de l'échange de chaleur dans le refroidissement des fruits et légumesInvestigating the factors for intensifying fruit and vegetable cooling

Increasing the rate of fruit and vegetable cooling is of economic significance for the following reasons: biochemical and microbiological processes are quickly suppressed; surface mass-exchange with ambient air is slowed down; power consumption is reduced, and the freezing output of cooling equipment and installations is increased.It was assumed that the fruits and vegetables in crates were arranged regularly and covered with thin paper of a negligible small thermal resistance in order to eliminate the infiltration of cold air within the layers. Crates were arranged on a pallet so that they touched horizontally. Thus, the packages form plates above and below the cooling air flow. Heat-exchange with a one-dimensional temperature field is established.It was found that intensification of cooling can be achieved by increasing the speed of cooling air as well as by stopping the process at a higher final temperature. Increasing the speed up to 5 m s^?1 shortens the time of the process by a factor of two compared with the low speeds (0.3–0.5 m s^?1) which are normally used. The product can be cooled until the temperature in the layer centre reaches 5°C, and the surface temperature about 2°C, which is low enough. Afterwards the cooled product is transferred to a freezing chamber or to a van-freezer. This factor results in a further halving of the cooling time. The combined effect of the two factors shortens the duration of the process by about 75% and increases the output of the cooling equipment from 3.5 to 4 times.     

热害矿井空气能系统降温与废热提级利用系统设计

针对目前热害矿井在开采过程中存在的危害,各国针对存在热害的矿井采取了不同的防治措施,并且取得了一定效果,但是其系统的投资与运行费用较高。提出一种利用空气能系统对矿井进行降温的新模式,结合平顶山大庄矿矿井基本情况,对机电硐室进行空气能制冷降温与废热提级利用系统设计,并对主要设备进行了选型。最后与传统冷水机组制冷降温系统进行比较,空气能系统具有显著的经济效益。研究成果为企业节能减排方案的选择提供了参考和依据。     

Utilization of LNG coldUtilisation du froid du GNL

This paper will discuss the utilization of LNG cold in Japan. Discussion is concentrated on the following: temperature conditions of both direct and indirect utilization; restriction in quantity and mode of cryogenic energy utilization; distance from LNG terminals to cold utilization plants; cooling system for LNG cold utilization plants, and emergence of cryogenic energy utilization complexes.     

Refrigeration machinery - a review

The paper gives a survey of several developments in the field of refrigeration which are of specific interest to Commission B2 of the IIR. The report is divided into the following sections: compression machines; absorption machines; expansion machines; thermo-electric cooling; vortex-tubes; heat pumps; refrigeration media; driving systems; and air cooled equipment.     

Heat and mass transfer analysis in air-cooling of spherical food productsTransfert de chaleur et de masse dans le refroidissement par air des aliments sphériques

The one dimensional transient heat conduction equation, in spherical co-ordinates, is solved with convective surface boundary condition, during air-cooling. The enthalpy potential concept is used to include the cooling effect of desiccation. A calculation scheme is proposed in which, up to half the cooling time, the calculation is made with both heat and mass transfer from the product surface, thereafter it is continued with heat transfer only. The calculated temperatures for apples and potatoes are compared with the measured values available in the literature, and good agreement is observed.     

European research on solar-assisted air conditioning

The utilization of waste heat, on the one hand, and solar heat, on the other, in order to energize sorption chillers is an important issue for increasing the energy efficiency of cooling machines. Especially in the air-conditioning business, a tight correlation often exists between insolation and cooling requirements. Therefore, the interest in solar cooling by sorption systems has prevailed for several decades. Some hundred systems have been installed all over the world and operate satisfactorily. However, no really cost-competitive system for widespread application exists. A step forward can only be expected by innovative design of the collectors, chillers, or both.This paper reports on trends which might lead to such innovations. The sources are mainly papers and discussions at workshops held in 1994 in Dresden and 1995 in Freiburg and Garching, Germany. Although in these workshops mainly European experiences have been discussed, the conclusions are valid world-wide: generally, it can be stated that several new ideas, both in collectors and chillers, have gained ground. Cheaper collectors providing higher temperatures have become available and specially designed chillers for use with low-grade heat as input are being investigated.In this paper we highlight the most important developments reported on in the workshops mentioned above.     

Solar absorption cooling effect on operational parameters on power savingRefroidissement par absorption à énergie solaire; influence des paramétres de fonctionnement sur l'économie d'électricité

The paper deals with engineering estimates of the electrical power consumption of equivalent cooling capacity vapour-compression and vapour-absorption (solar) cooling systems. The effects of operational parameters on absorption chiller performance have been studied to define the breakeven point at which the two systems will consume equivalent amounts of electrical energy per unit of cooling output.     

孔庄煤矿集中降温方案的选择与优化

从孔庄煤矿井筒布置和矿井生产条件出发,先后总结、分析了片冰降温系统、热-电-乙二醇降温系统、井下低温水排热的井下集中降温系统(HEMS)和真空制冰降温系统。从集中降温方案效果、投资、降温系统运行稳定性、井筒输冷管路安装、矿井制冷水质、井下制冷排热等方面综合考虑,适合孔庄煤矿特点的集中降温途径只能是真空制冰降温方案,为矿井三期改扩建工程按期投产、验收创造了条件。同时,该降温工程的实施必将填补我国在矿井集中降温领域的一项技术空白,并在制冰技术、输冰管道、输冰工艺、压风冷却、井下融冰工艺、制冰节能技术上取得突破,进而推动我国煤矿降温制冷工艺的创新和发展。     

Energy conservation in environmentally controlled facilitiesEconomies d'énergie dans les installations à environnement contrôlé

Factors governing energy costs in the operation of refrigerated warehouses are discussed. Electrical demand must be controlled to achieve the cheapest rates within the conditions of the electrical supply contract. Cold store layout should be designed for logical storage of material between different temperature zones. Refrigeration demand is kept low not only by using the optimum thickness of insulation but by equal attention to water vapour inflow and air infiltration. Equipment choice is also crucial, together with good maintenance.     

利用昼夜温差的太阳能电水联产系统

太阳能作为一种清洁无污染,取之不尽用之不竭的能源越来越受到人们的关注。太阳能光伏发电是现今太阳能利用的主要方式,在光伏发电过程中如果硅板散热不好将使得硅板温度的上升,从而导致发电效率降低。针对此,我们小组提出了基于吸附式制冷的电水联产系统,利用沙漠昼夜的巨大温差,通过水的蒸发解决硅板散热问题,且在夜间进行空气取水。该系统结构简单,稳定可靠,无能耗无水耗,既解决太阳能发电的硅板散热问题,又可制水供缺水地区生活所用。     

Heat pumps: trends and possibilities

The recent developments in heat pump technology have been prompted by a change from using refrigerating machines to real heat pump design. The compressor must be built for higher pressures and higher pressure ratios. The drives of heat pump compressors are not only electrical motors but are also diesel or gas-energized motors. This gives a large change in primary energy consumption. For all types of drives there is a tendency towards varying speed for capacity control. Electrical motors can do it by a change of frequency whereas combustion engines can change the speed un to 3 : 1 without any hard change of relative energy consumption. Higher speed ratios are sometimes very critical for the suction- and dischange-valves of the piston compressors. Therefore it is necessary to look for on-and-off control with a short-time heat storage.In several parts of the world investigations are going on into the influence of suction gas cooling on the energy consumption of heat pumps. A wide range of refrigerants and refrigerant mixtures must be considered as suitable for heat pumps.Quite a large field of development is in the area of thermal heat pumps. The absorption refrigerating machine is very well known but for heating purposes, new system designs and especially new working couples are necessary. Even with knowledge of the criteria for the refrigerants and solvents, it will be hard work developing optimal substrates. Beside advances in adsorption machinery there will also be developments in the fields of adsorption and resorption heat pumps. Looking towards total energy systems Rankine-cycle heat pumps are of great interest.The applications of heat pumps lie not only in low temperature heating with air, water or earth as the heat source, but also in a wide range of heat recovery systems for industry. In future the temperature range of industrial heat pumps will be going up to 573 K (300°C) or more. The development of heat pumps and their applications is in its infancy. There will be a lot of work to be done. Let us do it.     

LNG and world energy needs. Part 1: Gas liquefaction and world resourcesLa liquéfaction des gaz et ressources mondiales. 1e partie: les GNL et les besoins mondiaux en énergie

The development of international trans-shipment of LNG will be reviewed, comparing the present achievement with the world potential. The scope for further development will be discussed together with the problems that delay it.Base-load liquefaction plants have already achieved a high level of efficiency and reliability, and the possibility of major improvement has become small. Present technical interest centres on the practicability of offshore liquefaction, including the problems of liquefaction on a floating barge, floating storage and flexible pipeline systems for LNG transfers.Land-based LNG storage systems have developed greatly, especially in Japan, where important strides have also been made in utilising the ‘cold’ available from re-evaporation. Whilst significant developments have been made with both above-ground and in-ground storage the present preferences appear to lie with a compromise solution involving an insulated tank partially submerged in the ground, the excavated earth being mounded around the tank up to the level of the tank top.There are now fleets of ocean-going tankers for LNG, and a few are laid-up awaiting charter. The largest has a capacity in excess of 130 000 m³. Several different insulation systems are employed, the criteria being cost, evaporation losses and safety. Much attention is being devoted to the elimination of hazards which could arise with shipping accidents.Other uses of LNG are relevant to energy conservation on a smaller scale. These include peak-shaving plants, the enrichment of lean natural gas, satellite stations and diurnal storage.