Sustainable development has become a key concern in industries, largely due to natural resource depletion, global competition, environmental pressure, etc. Despite the efforts for sustainability improvement, still over a half of energy consumption is wasted in manufacturing sectors, where the chemical industry is responsible for the energy efficiency lower than it should be. Many attempts have been made to recover the thermal energy using heat integration techniques. Although work is more expensive than process heat, no efficient solution has been studied to recover mechanical energy yet. In chemical plants, many process streams need to be pressurized or depressurized in different operational stages. Therefore the energy of these streams can be recovered by a new class of exchange, which is called work exchange (Huang and Fan, 1996). Two possible ways to exchange mechanical energy between two streams are direct and indirect recovery devices.
Some studies related to indirect recovery devices, such as single-shaft-turbine-compressor (SSTC) units, have been reported, where a superstructure-based Work Exchange Network (WEN) synthesis has been introduced (Razib et al., 2012). The direct recovery of mechanical using Work Exchanger as a key device is still at the stage of analysis. In this paper, the technical feasibility and thermodynamic efficiency of these two types of the work exchange units are discussed in details. Sustainability assessment with the main focus on the energy recovery efficiency and cost analysis, beside the safety of these two type of WE’s, is introduced. Indirect recovery devices like SSTC are traditional compressors and turbines with a mature technology and known capital cost data. Direct recovery devices are pair of combined operated piston pumps without any accurate capital cost data which needs to be estimated in the presented work. The possibility of work and heat integration through direct work exchange units for non-isothermal and adiabatic operating conditions is the other parameter which is analyzed. Mechanical energy recovery using different types of units are compared through a case study.
Huang, Y.L. and L.T. Fan, “Analysis of a Work Exchanger Network,” Ind. Eng. Chem. Res., 35(10), 3528-3538, 1996.
Razib, M.S., M.M.F. Hasan, and I.A. Karimi, “Preliminary Synthesis of Work Exchange Networks,” Comp. & Chem. Eng., 37, 262-277, 2012.