Luma M. Diab and Farayi Musharavati
Abstract In dual purpose power and water (DPPW) production plants two challenges are often encountered; (a) maintaining operations that meet a desired water production/demand ratio or power production/demand ratio, and (b) meeting the desired water to power ratio. Although these problems are usually implied in the implemented plant design and technology, operational issues play an important role in fine tuning operations towards optimal performance. In addition, operational practices have a bearing on energy consumption and operating efficiencies. In this study, a simulation based approach is used to provide data for handling the fine tuning of operations towards desired targets. To this end, numerical simulation is used to determine the relationships between total water/power demand and total water/ power produced. In order to reduce the specific energy consumption of the plant, investigations on the design and operating features of the DPPW production plants were carried out. An existing DPPW production plant was used as a case study. The investigation proceeded by focusing on identifying the optimal production operation strategies that, if implemented, can reduce energy consumption in the production of water and power. Discrete event simulation was used to experiment with a number of feasible plant configurations and strategies for producing power and water. Water to power ratios were used to compare the effectiveness of the feasible production operation strategies through simulation experiments. For each configuration, average values of the simulated data (i. e. both water and power) were determined and used to calculate water to power ratios. Simulation results show that different plant configurations and different operational strategies and practices affect the water to power ratios. This allows engineers and operators to select plant configurations, operational strategies and practices that give them the desired water to power ratios
F. Musharavati (H) ■ L. M. Diab
Department of Mechanical and Industrial Engineering,
Qatar University, PO Box 2713, Doha, Qatar e-mail: farayi@qu. edu. qa
L. M. Diab
e-mail: Luma_diab89@windowslive. com
I. Dincer et al. (eds.), Progress in Sustainable Energy Technologies: 725
Generating Renewable Energy, DOI 10.1007/978-3-319-07896-0_46,
© Springer International Publishing Switzerland 2014
with respect to demand scenarios. Therefore, simulation is an effective tool in identifying opportunities for tuning operations to meet desired production requirements.
Keywords Simulation modeling • Numerical simulation • Discrete event simulation • Dual purpose power and water (DPPW) production • Desalination • Water/power ratios
Power and water production are among the most important factors that facilitate the developmental process of a national economy . To date, dual purpose power and water production plants have been accepted as one of the feasible solutions for providing freshwater and electricity in arid and semi-arid regions. Consequently, a lot of research has been done to improve, upgrade and advance the thermodynamic efficiencies of the various technologies used in dual purpose power and water production plants [2–5]. Unlike most of these research attempts that focus more on capital intensive projects, the research presented in this study aims to identify non-capital intensive initiatives for improving operating performances. More specifically, this study focusses on using general purpose simulation as a tool for providing process plant data for fine tuning operations to desired targets and improved operating efficiencies.
In the operations of DPPW production plants, two challenges are often encountered, namely; (1) meeting the desired or an optimal water to power ratio, and (2) maintaining operations that meet either a desired or an optimal water produc – tion/demand ratio or power production/demand ratio. Problems associated with these challenges usually arise as consequences of operational issues and practice. As such, these challenges can be addressed by identifying and implementing; (a) suitable plant configurations, and (b) optimal production operation strategies. Implementing suitable plant configurations allows operators to engineer plant performance towards optimum water to power ratios. On the other hand, implementing optimal production operation strategies often results in significant improvements in operating and energy efficiencies. In this study, the challenges mentioned above are addressed through a simulation based approach. A case study of an existing DPPW production plant in Qatar was used to identify optimization initiatives for improving operating efficiencies and reducing production costs in the operations of dual purpose water and power production plants.
A number of possible configurations and arrangements of the DPPW production systems can be achieved in practice. For case study plant considered in this study, power generation is driven by gas turbines and thermal energy from their exhaust are used to generate low-to-medium pressure steam in waste heat recovery boilers. Steam is routed directly to the brine heater of a multi-stage flash (MSF) distillation plant. Auxiliary boilers are used in order to achieve higher yields.
The power to water ratios produced by various conventional DPPW production systems depends on plant design . It has been shown that different plant designs are associated with a specific range of power to water ratios. For example, extraction turbine systems can give between 8 and 15 MW/MIGD, back pressure turbine system can give between 3 and 6 MW/MIGD and gas turbine systems can give between 8 and 20 MW/MIGD. The significance of the power to water ratios lies in that fuel savings tend to increase with decreasing power to water ratio . In practice, the demand of power and water varies either by time of the day, month of the year and also by the general increase in population as well as the growth and development of the industry. These variations often require fine tuning of operations within design limits. In other circumstances, large variations may require a corresponding change in the plant design or plant design parameters. Each of the changes made may be associated with changes in operating and energy efficiencies. The changes made may also have a bearing on the energy consumption in the plant. As such it is necessary for operators to make informed decisions. One way of availing decision information is to use simulation.
The aim of this study is to use simulation to identify, evaluate and assess optimization initiatives for improving operating efficiencies and reducing production costs in DPPW production plants. Simulation models can then be used to explore and investigate the performance of the plant operations under different conditions and scenarios. In order to achieve the aim mentioned above, the following specific objectives will be addressed:
• To model and simulate the relationship between total water (power) demands and total water (power) produced in a bid to characterize production-demand scenarios
• To model and simulate production operations strategies in order to identify optimal operating strategies based on the power to water ratios.
In the analysis, improvements on operating efficiencies were based on; (i) analyzing energy savings related to an optimal match of the power to water ratio, and (ii) identifying optimal operating scenarios, states and parameters for improving operating efficiencies. Achieving such improvements often translate into reducing consumption of primary fuel and fresh water utilizations in power and water production plants while at the same time meeting the electricity and desalinated water requirements for consumers. In addition, implementation of the results of this study can go a long way in positioning an organization towards operational excellence. This would also allow the organization to benchmark and or compare its operations with the highest industry standard on operational efficiency. Moreover, improving operational efficiencies usually involves adopting flexible organization structures that allow for a network flow of information. This would also involve other stakeholders, such as the suppliers, distributors and customers along the supply chain. The remainder of this paper is organized as follows; simulation methods used in this paper are described, followed by an outline of the results of the simulation based study and finally concluding remarks are discussed.