Dong Gil Shin

Optimization Study on the Performance Analysis of Organic Rankine Cycle for Characteristics of Low Temperature Heat Sources

Optimization procedures of performance analysis for ORC(Organic Rankine Cycle) system are established to the characteristics of low temperature heat sources such as open-type and closed-type. Effective heat recovery and heat extraction related to maximum power of the cycle as well as heat quality and thermal efficiency must be considered in the case of the open-type low temperature heat source. On the other hand, in the case of the closed-type low temperature heat source, only thermal efficiency is important due to constant heat input. In this study, thermal efficiency and exergy efficiency representing a level of close to Carnot cycle are studied, as useful index for the optimization of the ORC system. To validate the results of cycle analysis, those are compared with appropriate experimental data of ORC system as a thermal efficiency point of view.

Operating Characteristics of a Scroll Expander Used in Organic Rankine Cycle

ABSTRACT:The rapid increases in global energy demand and global warming need renewable energy sources such as solar thermal energy, biomass energy and waste heat. A ORC-based micro-CHP system(< 10 kWe) is one of the effective means to use renewable energy and solve energy problems because of its compactness, flexibilities and lower cost compared to other systems. The most important core components of the ORC is the expander which has a strong effect on the cycle efficiency. In the range of power output from 1 to 10 kW, the scroll expander is a good choice due to its performance and reliability. In this study, we have carried out an experimental study on an ORC equipped with oil-free scroll expander working with refrigerant R134a. We have measured power output and thermal efficiencies of the ORC and analyzed correlation between volumetric efficiencies of the expander and thermal efficiencies of the ORC.Keywords:Renewable energy(신재생에너지), Micro-CHP(초소형 열병합발전), ORC(유기랭킨사이클), Scroll expander(스크롤 팽창기)

Flue Gas Waste Heat and Water Recovery Organic Rankine Cycle

Extended Abstract Fossil fuel-based power plants consume significant amount of water. Therefore, the power plants can cause an environmental impact and its locations are very limited by the availability of water. Water recovery from flue gas in the power plants could contribute to reduce water requirement. For example, a 600MW coal power plant releases 45 ton/min of flue gas including 7.2 ton/min of moisture [1]. Several technologies including water condensation by cooling water [1], liquid desiccant dehumidification system (LDDS) [2], and transport membrane condenser (TMC) [3] have been developed. In this study, in order to condense the moisture in flue gas, the flue gas is firstly cooled down by a waste heat recovery (WHR) organic Rankine cycle (ORC) system and is further cooled down below dew point (55°C) by a pumped heat pipe cooling loop combined with the ORC system. Two-phase cooling by the organic working fluid instead of cooling water can reduce the large surface area [4] of condensing heat exchanger for low-temperature flue gas. Furthermore, an ejector cooling system or vapor compression refrigeration system driven by the waste heat of flue gas [5], combined with the ORC system, can be used to further cool down the flue gas because it is very difficult to condense the moisture in the flue gas with a high ambient temperature. In the case of the 600MW coal power plant releasing 150°C of flue gas, the WHR ORC system can produce about 6.7MW of additional power and recover 50% of water in flue gas by cooling the flue gas to 40°C at the evaporation temperature of 30°C for R134a. Furthermore, with the help of the vapor compression cooling system driven by the heated high pressure working fluid, it can recover 70% of water in flue gas by cooling the flue gas to 30°C at the evaporation temperature of 20°C for R134a. Along with the water recovery in the condensing heat exchanger, condensable particulate matter (CPM) can be separated from the flue gas for environmental friendliness [6,7].

Experimental Study of Vane Expander Prototype Applied to Micro Organic Rankine Cycle

In this study, performances of the vane expander protype for micro organic Rankine cycle with refrigerant R134a as a working fluid have been analyzed. While operating organic Rankine cycle for analysing expander efficiencies such as overall efficiencies, volumetric efficiencies and mechanical efficiencies under of expander inlet temperature, the power of the expander, inlet temperature of expander, inlet pressure of expander and the flow rate of the working fluid(refrigerant R134a) have been measured while varying the rotational speed of the expander. It was found that the more the expander revolution speed is high, the more the expander power, overall efficiencies and volumetric efficiencies are higher. In case of 500 rpm of rotational speed, overall efficiencies are 6~7% and in case of 1000 rpm, overall efficiencies are 11~12%. We have found that low volumetric efficiencies result in poor overall efficiencies.

Optimization of Design Pressure Ratio of Positive Displacement Expander for Engine Waste Heat Recovery of Vehicle

The effect of built-in volume ratio of expander on the performance of a two-loop Rankine cycle system for engine waste heat recovery of vehicle has been investigated. In the case of positive displacement expander in the various operating condition of the vehicle, it can operate in both under-expansion and over-expansion conditions. Therefore, the analysis of off-design performance for the expander is very important. Furthermore, the volume and weight of the expander as well as the efficiency must be considered in the optimization of the expander. This study shows that the built-in volume ratio of expander causing under-expansion at a target condition is more desirable considering the off-design performance and size of the expander, based on the simple modeling of off-design operation of the expander.

THERMODYNAMIC ANALYSIS OF A CLOSED BRAYTON/ERICSSON CYCLE ENGINE WITH SCROLL MACHINES

Stirling and Ericsson engines have great potential for many applications, including micro-cogeneration, solar power, and biomass. However, ideal cycles of both types of engines are difficult to achieve in practice because neither isothermal compression nor isothermal expansion is practical with reciprocating piston engines or with turbomachinery. On the other hand, scroll compressor and expander can be very suitable for effective cooling and heating because of the high area-to-volume ratio of scroll geometry or the application of two-phase flow. To achieve quasi-isothermal compression, either a large amount of liquid is injected into the inlet of the compressor or the compressor is externally cooled by liquid. Similarly, for quasi-isothermal expansion, either hot liquid, such as thermal oil, is injected into the inlet of the expander or the expander is externally heated by a heat source. In this current study, we have undertaken a theoretical investigation of thermodynamic analyses of several kinds of scroll-type engines, in particular with regard to associated compression and expansion processes, adiabatic or quasi-isothermal processes, and the highest cycle temperature. We selected power density, or thermal efficiency, as an objective function, and then deduced optimal design parameters for the scroll-type engine.