The design of a small-scale multi-stage desalination plant driven by the exhaust of diesel generators

Abstract

The present study provides an energy-saving design of a desalination plant that uses the waste heat of the exhaust of a diesel generator. The proposed model consists of a multistage flash (MSF) desalination unit in which the sea water is heated by the flue gases instead of steam. A mathematical model is derived to design the entire plant including the waste heat recovery heat exchanger and the MSF plant. The model is flexibly designed in order to deal with wide range of diesel generators rates and any number of stages of MSF. A database of diesel generator sets are imported including temperature of exhaust, gas flow rates and the back pressures for each set. Two test cases are carried out with two different salinity levels and diesel generator rates, results show that the amount of distilled water in kg/s can be correlated to the rate of diesel generator according to the second order polynomial: 0.54 + 4.1 x 10-3 (kVA) + 4.1 x 10-6 (kVA) 2 in the case of brackish water and 0.36 + 2.7 x 10-3 (kVA) + 3.1 x 10-6 (kVA) 2 in the case of seawater. The survey of power generation in Lebanon reveals that the waste heat from a diesel generator can be utilized to get around 100 million m 3 of distillate water usable for drinking and for domestic use. This quantity can provide fresh water for more than 300,000 person/year. The performance of proposed plant is assessed during summer and winter conditions and the model can deal with any salinity ranges.

Numerical and Experimental Study of a Multi-Generation Desalination Power Plant

“…It was concluded that the amount of freshwater produced by a diesel generator could be estimated by the second order polynomial as 0.36 + 2.7 × 10 −3 (kVA) + 3.1 × 10 −6 (kVA) 2 [19]. Table 6 shows the values determined in the other case studies and validates the proposed small scale multigeneration desalination design as a viable option for producing power and fresh water.…”

“…In a combined cycle cogeneration design the net power that is produced equals the sum of all the power within the system as denoted in Equation (19). This includes: gas turbine power output (positive), compressor power input (negative), steam turbine power output (positive), and pump power input (negative) [20].…”

“…The numerical analysis presented below is based on a set of industry standard assumptions that do not significantly impact the results [19]. The following assumptions are made:…”

“…Shafaghat and Kotb studied the optimum design for multi-stage flash (MSF) desalination coupled with power plants of 42 MW and 650 MW respectively [17] [18]. Finally, Jammoul and El-Samni investigated the design and benefits of a small scale MSF desalination unit driven by the exhaust of diesel generators [19]. The last three studies are used to validate the proposed design in this paper and a comparison analysis will yield a better understanding the challenges for small scale multigeneration.…”

Design and Energy Requirements of a Photovoltaic-Thermal Powered Water Desalination Plant for the Middle East

“…This creates a seasonal effect on the quality of water produced from this process. Researchers have concluded that production is higher in summer than in winter due to the higher summer feedwater temperatures [10].…”