Deep Water Cooled ORC for Offshore Floating Oil Platform Applications

Abstract

Due to global warming, environmental pollution and cost reduction, increasing efficiency of electricity conversion has become a key issue for the offshore market. This paper proposes an Organic Rankine Cycle (ORC), which uses heat waste from exhaust gases of an FPSO (Floating, Production, Storage and Offloading unit) as heating source, and deep ocean water as cooling source. A genetic algorithm optimization was conducted targeting maximization of net power output, by taking in to consideration of 23 working fluids. Expander inlet temperature and pressure were set as independent variables. The analysis encompasses subcritical or supercritical conditions and recuperation was included in a second version of the system as an option. The first configuration presented ethanol as optimal fluid, followed by toluene and the second configuration indicated cyclohexane followed by ethanol. Use of recuperation, when feasible, increased power output specially for cycles operating with dry and isentropic fluids, presenting an average contribution of 22.7%. Net power and efficiency results from ORC using deep sea water in condenser were presented and compared with ORC using shallow ocean water as cooling source and with Carnot efficiency operating under the same temperatures. Use of deep water raised net power output by 23.3% (cyclohexane recuperative ORC) and 12.5% (ethanol non-recuperative ORC) for the optimal configurations.

Thermoeconomic Optimization with PSO Algorithm of Waste Heat Recovery Systems Based on Organic Rankine Cycle System for a Natural Gas Engine

“…Toluene was used as a working fluid, taking into account the good cost-benefit ratio that this offers for the system integrated with the engine gases. The parameters considered for the study of the system were isentropic efficiencies for the turbines of 80%, isentropic efficiencies for the pumps equal to 75% [17], the temperature of the cooling water in line 1A is 50 °C, The operating conditions and thermoeconomic analysis of the SORC, RORC, and DORC models were determined, as well as taking into account a secondary circuit of thermal oil for a real operating context of the analyzed engine. In the most frequent operating conditions, the inlet is gas flow (120 L/min), λ (1.784), engine revolutions (1842 rpm), gas pressure (1163.6 mbar), the throttle valve is open at 80%, while the turbo bypass valve is open at 9.1%, the gas is at a temperature of 389 • C, and the coolant temperature is 63.9 • C. The outputs for this engine are 1758 kW with an effective efficiency of 38.59%, the heat recovery efficiency of 40.78%, the heat removed from the exhaust gas is 514.85 kW, and the specific fuel consumption is 177.65 g/kWh [15].…”

“…Toluene was used as a working fluid, taking into account the good cost-benefit ratio that this offers for the system integrated with the engine gases. The parameters considered for the study of the system were isentropic efficiencies for the turbines of 80%, isentropic efficiencies for the pumps equal to 75% [17], the temperature of the cooling water in line 1A is 50 • C, pinch point of the condenser 15 • C, pinch point evaporator ITC2 and ITC4 (35 • C), and efficiency in the recuperator of 85% [17]. In the base case, the pressure ratio in B1 and B2 are 2.5 and 30, respectively, for the SORC and RORC models, while in the DORC pressure ratios of 11.09, 20, 20, for B1, B2, and B3 were used in that order.…”

“…Acceleration is weighted by a random term with separate random numbers generated for acceleration to pBest and gBest locations. Particle updates are performed according to Equations (16) and (17) [27].…”

Thermoeconomic Analysis of Different Exhaust Waste-Heat Recovery Systems for Natural Gas Engine Based on ORC

“…The determination of the operating conditions and thermoeconomic analysis of the SORC, RORC and DORC configurations, including the thermal oil secondary circuit, is performed for a real operating context of the engine under study. In the most frequent operating condition, the input values are gas flow (120 L/min), λ (1.784), engine revolution (1482 rev/min), gas pressure (1163.6 mbar), throttle valve (80%), turbo bypass valve (9.1%), gas temperature (389 • C) and engine coolant temperature (63.9 • C), and the outputs are mechanical engine power (1758.77 kW), with an effective engine efficiency (38.59%), heat recovery efficiency (40.78%), heat removed from exhaust gases (514.85 kW) and specific engine fuel consumption (177.65 g/kWh) [10,27,28]. To take advantage of the thermal availability of the waste gases (state 10), the simple ORC (SORC), ORC with recuperator (RORC) and double-pressure ORC (DORC) configurations have been adopted to generate additional power as shown in Figure 2 [7,10,25,26].…”

“…Cyclohexane was selected as the working fluid, considering the cost-effective performance in this system integrated with the gas engine. The parameters considered to study the systems in the configurations were isentropic efficiency turbines (80%) [28], isentropic efficiency pumps (75%) [28], cooling-water temperature in stream T1A (50°C), pinch-point condenser (15 °C), pinch point evaporators ITC2 and ITC4 (35 °C) and effectiveness in the recuperator (85%) [28]. Pressure ratios in B1 of (2.5) and B2 (30) were considered in the SORC and RORC systems, while in the DORC the pressure ratios were B1 (11.09), B2 (20) and B3 (9).…”