Analysis Of Refrigeration System Utilizing Waste Heat On A Ship

1.0 Introduction

1.1 Background To The Study

Maritime transport is a huge energy-consuming sector globally. Typically onboard energy is produced using diesel engine combustion. This power is used for propulsion and to generate electricity that is needed onboard. However, environmental and economic concerns have caused the maritime sector to explore alternative solutions in order to improve the efficiency of the energy usage system and to reduce their emissions. Diesel engine combustion produces pollutants like SOx and NOx [1]. Approximately 3.3% of global CO2 emissions are caused by shipping. The International Maritime Organization is the major global regulator for emissions in maritime transport. Moreover, the European Union has implemented a directive for sulfur emissions in specific control areas. These factors and the fact that the prices of fossil fuels are rising continuously have motivated the marine sector to reduce its fuel consumption [2]. Baldi and Gabrielii [3] described a methodology for performing a feasibility analysis of the installation of a waste heat recovery (WHR) system on a vessel. The method based on available data from ship operational profile. The various types of WHR technologies available on board ships were discussed from the perspective of technological principle and application feasibility by Shu et al. [4]. The focus was to provide a better understanding of the options available for WHR in order to improve fuel economy and environmental compliance.

A simulated study for a waste heat powered water-LiBr absorption cycle cooling system for a cargo ship was made by Cao et al. [2]. Several core components of a cooling system were modelled and validated. They used the data of a ship that was equipped with a WARTSILA 8RT-flex68-D engine for propulsion. The rated capacity of the engine was 25,040 kW. The single effect refrigeration system was simulated for space cooling. Heat was recovered by an economizer in a flue gas flow, using a circulating hot water cycle. Hot water was used as a heat source for the generator after which it is used for hot water production to meet shipboard hot water demands (residential, kitchen, and clinic demands). Both the condenser and the absorber were cooled with sea water. The chilled water cycle was cooled in the evaporator and the space cooling power was transferred to a heat exchanger to the mixture of outdoor air and recirculated indoor air. The simulations were done under Miami conditions.

The resulting COP is 0.64 for the absorption refrigeration cycle and for the whole system it was 0.6. The ship’s fuel consumption and the CO2 emissions were 62% less compared to vapor compression. The simulation was also done for weather conditions in Abu Dhabi and Baltimore. The fuel consumption and CO2 emissions reductions increased by up to 68% under warmer conditions (Abu Dhabi) compared to vapor compression. However under colder conditions (Baltimore) they decreased to 38%. The simulation result was also applied to a cruise ship, where the cooling demand is higher, and an 8.23% total energy consumption reduction (the fuel saving share) was found compared to vapor compression.

If the heat energy possesses the advantage to be “clean”, free and renewable, then this is probably considered as an adapted potential solution, which answers in even-time at an economic pre-occupation and ecological problem. Among the main research done, it is found that refrigeration system uses this free and renewable source. Among all the domestic and industrial appliances used today, refrigerators consume a considerable amount of energy. Using heat energy to run refrigerators is of great practical relevance nowadays.

The recovery of waste energy or waste heat recovery is heat, which is produced in a process by way of fuel combustion or chemical reaction and then dumped into the environment, even though it could still be re-used for some useful financial resolutions. In water cooled engines, the one third of the energy is wasted in exhaust gases. For such cases, vapour compression air conditioning system is used for cooling of cabins and in preservation of goods on board a ship.

At present, some effort has been devoted to the utilization of the vast amount of waste energy from diesel engines used aboard ships for refrigeration. There are several types of refrigeration technology being used for marine applications, including compression refrigeration, sorption refrigeration, and injection refrigeration. It needs extra energy to drive the compression and injection refrigeration systems, which leads to the increase of fuel consumption of ships. A sorption refrigeration system is driven by thermal energy and needs little electricity, and it can utilize the waste heat of the engine and improve the energy conversion efficiency. Therefore, fuel can be saved considerably. Both absorption and adsorption refrigeration are sorption refrigeration technologies

1.2 Statement Of Problem

Refrigeration plays a vital part in the preservation of perishable cargoes and provisions for the crew onboard vessels. In merchant vessels, the temperature of victuals and cargoes such as food, chemicals, liquefied gas etc. are controlled by the refrigeration plant of the ship. The main purpose of ship refrigeration plant is to prevent loss of the cargoes or perishables so as to ensure their safe transportation in good and healthy condition (Anish, 2016).The potentials inherent in converting heat and wasted energy from exhaust gas of ships is on the high. This firstly, mitigation of environmental pollution is applied here and a VAR type system can be supplied with this energy since they are mainly low grade energy and consist of mainly heat. Instead of allowing this waste heat to cause environmental hazards, the study examines how this heat can be converted to aid refrigeration by increasing the coefficient of performance (COP) of the system by utilizing waste energy.

1.3 Purpose Of The Study

The main aim of the study is to analyze the refrigeration system utilizing waste heat on a ship. The process data of the exhaust gases and cooling water flows in different climate conditions and operation profiles is studied to estimate the refrigeration potential for ships in general.

1.4 Scope Of Research

The scope of this research work focuses on the design analysis of cooling system for a ship, using waste heat of the engine exhaust, without much effort on the engine performance.