Thermodynamic analysis of solar integrated waste heat recovery systems for power generation industry using eco-friendly fluids

This paper explores eco-friendly material R134a and activated carbon-methanol based organic Rankine model and solar integrated vapor adsorption cooling system for waste heat utilization of condenser unit of steam power plant. The results of proposed model analysis is to explain the environmental parameters of used material, effect of operating parameters and cooling-power output. The proposed analysis is concern with the condenser heat recovery of reheating-Rankine steam power plant by using eco-friendly material based ORC and vapor adsorption cooling system for simultaneously power and cooling generation. Two models have been analyzed in this paper, model-1 (Fig-1) integrated with solar ORC and model-2(fFg-2) equipped with double bed adsorption refrigeration system.Model-2 have two different adsorbed bed. Bed-1 is connected with condenser outlet of reheating-Rankine steam plant and AC-Methanol material pair is used and bed-2 integrated with solar parabolic collector for condenser water heating, that heated water circulating to bed-2 for generator purpose. The main objective of this analysis to estimate the multiple thermal effect (heating-power and cooling) from available un-covered heat of power plant by using different novel thermal system. The application of R134a and AC-Methanol type material helps to produce required cooling effect at low grade of thermal availability with environmental safety aspect. 


Introduction

The uncovered heat from power plants and heavy industry is dumped into atmosphere and it causes of severe impact on atmosphere in terms of greenhouse effect. The US Dept. of Energy reported that the cement/ captive power plants have, nearly 35% heat is lost, and this corresponds to around 70 to 75 MW of thermal energy. 
EPA estimated that the 65% of world CO2 emission is recorded from greenhouse gas emission from fissile fuel burning during intensive industrial process. This un-used or waste heat have tremendous potential to generate heating-power and cooling generation for industrial process by using eco-friendly material based novel thermodynamic system like, organic Rankine system (ORC), kalina system for cooling-power generation, vapor absorption and adsorption refrigeration techniques. The employment of solar energy will enhance the system performance. All these systems work as waste heat recovery generator (WHRG). For a 6000 ton per day (tpd) capacity of cement plant can be reduced around 70,000 ton/annum of CO2 by installation of WHRG. 
The proposed analysis is concern with the condenser heat recovery of reheating-Rankine steam power plant by using eco-friendly material based ORC and vapor adsorption cooling system for simultaneously power and cooling generation. Two models have been analyzed in this paper, model-1 (Fig-1) and part description is given in Table-1(a) respectively. 

Literature Review 

The worldwide two major issues are being discussed in these days, CO2 concentration in atmosphere on one hand and energy crisis on other hand. All possible savings of reducing CO2 generation. Fossil fuels depletion, control in energy prices increments, achievable by adaptation of eco-friendly energy efficient material based technology. The un-arrested heat (waste heat) discharge from energy intensive industries like captive power plants, cement production, steel industry, Oil-refineries, etc have tremendous potential for multiple energy generation (heating-power & cooling) for further industrial process with dumped heat recovery [1-4] 
The numerous researches have been developed and analyzed eco-friendly material based novel thermodynamic model in environmental concern. The selection of a suitable working material depends on its great influence in the design of the process, application, heat source and the temperature level. The used material must have optimum thermodynamic properties at the lowest possible temperatures and pressures, and also satisfy several criteria such as economical, nontoxic, nonflammable, environmentally-friendly. An extensive literature review of R134a was chosen as working fluid. This selection has been done on the basis that R134a: is a nontoxic and nonflammable fluid and its Ozone Depletion Potential (ODP) is zero. R134a has a high molecular mass (chemical formula: CF3CH2F, MM=102kg/kmol).It has a temperature and critical pressure of 101.1ºC and 40.6 bar, respectively, R134a based heat recovery ORC of condenser operates at a higher pressure than atmospheric, and therefore air in-leakages do not occur. [1,2-4]. Several researchers have investigated the application and performance of ORC with R134a as a working fluid, the efficiency of the ORC using benzene, ammonia, R134a, R113, R11 and R12 was analyzed [5-7]. An analysis of a regenerative ORC based on the parametric optimization, using R12, R123, R134a, and R717 as working fluids superheated at constant pressure was carried out and. results revealed that selection of a regenerative ORC during overheating using R123 as working fluid appears to be a good system for converting low-grade waste heat to power [8]. In a low-temperature solar organic Rankine cycle system was designed and built with R134a as working fluid that works between 350ºC and 75.8ºC for reverse osmosis desalination in Greece, the results showed a system efficiency of about 7% and 4%, respectively [8-10]. Other studies that have analyzed the use of R134a as working fluid in the ORC cycles for reverse osmosis desalination at an experimental level [11], and also as a theoretical manner showed a simulation to estimate the increase in the efficiency and the energy available for desalination of an upper ORC coupled with a lower ORC with R134a, obtaining an efficiency for the latter of 4.2%. Other cycles with R134a for applications for geothermal sources are reported also and R134a integrated with internal combustion engine for heat recovery as bottoming cycle [12-21].The overall screening of all heat recovery fluids R134a was found to be the most suitable in terms of most eco-friendly, non-toxic, high thermal performance for cooling and power generation with optimized system. 
The other category of energy recovery material for green refrigeration technology as vapor adsorption refrigeration. Activated carbon is a form of carbon that has been pro­cessed to make it extremely porous, and it has a large surface area available for adsorption. Methanol and am­monia are the most common refrigerants paired with ac­tivated carbon. Activated carbon−methanol is one of the most promising working pairs in practical systems because of its large adsorption quantity and low adsorption heat (about 1800 to 2000 kJ/kg [22]. Low adsorption heat is beneficial to the system’s performance because the majority of heat consumption in the desorption phase is the adsorption heat. Another advantage of activated car­bon−methanol is low desorption temperature (about 100°C), which is within a suitable temperature range for using solar energy as a heat source[26].Activated carbon−ammonia has almost the same adsorp­tion heat as the activated carbon−methanol working pair. The main difference is the much higher operating pressure (about 1600 kPa when the condensing temperature is 40°C of activated carbon−ammonia. The high operating pressure leads to rather small pipe diameters and relatively compact heat exchangers, as compared to activated carbon− methanol. Another advantage of activated carbon−ammonia is the possibility of using heat sources at 200°C or above [23]. The drawbacks of this working pair are the toxicity and pungent smell of ammonia. Silica gel is a granular, highly porous form of silica made synthetically from sodium silicate. For the silica gel−wa­ter working pair, the adsorption heat is about 2500 kJ/kg and the desorption temperature could be as low as 50°C [22]. Such a low desorption tempera­ture makes it suitable for solar energy use with availability of 80-100 0C. One of the drawbacks of the silica gel−water working pair is its low adsorption quantity (about 0.2 kg water/kg silica gel). Another drawback is the limitation of evaporating temperature due to the freezing point of water [22-23]. Zeolite is a type of alumina silicate crystal composed of alkali or alkali soil. The adsorption heat of zeolite−water is higher than that of silica gel−water, at about 3300 to 4200 kJ/kg. The desorption tempera­ture of zeolite−water is higher than 200°C due to its stable performance at high temperatures. The drawbacks of zeolite−water are the same as for silica gel−water, low adsorp­tion quantity and inability to produce evaporating tempera­tures below 0°C [22]. 

This article is published in peer review journal and open access journal, International journal of research in engineering and innovation (IJREI) which have a high impact factor journal for more details regarding this article, please go through our journal website.








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