N.M. Al-Najem’s research while affiliated with Kuwait University and other places

In the first part of this study, it was shown that the use of nuclear option to fuel the cogeneration power desalting plants (N-CPDP) in Kuwait is more economical than the most efficient gas/steam turbines combined cycle GSCC using oil or natural gas. The power cost produced by N-CPDP was found to be at least 35% less than that of the GSCC. Furthermore, the use of fossil fuel in Kuwait would consume all of its oil reserves in less than 30 years if its present rate of fuel consumption prevails. The very high cost of oil fuel and the emission of greenhouse gases due to its burning (with its negative environmental effects) favor the use of nuclear energy. It was found that Kuwait, Saudi Arabia, Egypt, and United Arab Emirates satisfy the conditions required to consider the nuclear option in terms of: (1) needed additional power capacity, (2) needed seawater desalting capacity, (3) size of the electricity grid, and (4) the basic infrastructure required to build the N-CPDP. The use of a light water pressurized water reactor, the AP-600 (600 MW nominal power output), in N-CPDP was anticipated for Kuwait. This paper gives the details of the AP-600 steam cycle and its combination with thermal desalting plants with multi-effect distillation (MED), multi-stage flash (MSF), and thermal vapor compression (TVC) desalting systems. The water costs due to the coupling of MED, MSF, or TVC to the AP-600 nuclear power plant (NPP) were also calculated. Based on the required water-to-power ratio, either a back pressure steam turbine (BPST) or an extraction condensing steam turbine (ECST) was chosen. For the BPST, a maximum water-to-power ratio of 97 MIGD to 451 MW was obtained. Then, the use of ECST was chosen with a seawater desalting capacity of 50 MIGD. The results show that the cost of desalinating water with nuclear power is cheaper than that produced by fossil-fired plants, given the high cost of fossil fuel. Further, the estimated costs of producing electricity and water with MED+NCPP are lower than MSF+NCPP and TVC+NCPP. The unit product cost of the desalted water was calculated to be in the range of $0.87- 1.4 per m3 of product water based on a plant capacity of 227.3×103 m3/d. The presented technoeconomic results for the different desalination scenarios can help decision makers in choosing the best option that is suitable for the Kuwaiti conditions.

Gulf countries experienced rapid growth in the last four decades from oil production and its price increase. Natural water resources are very limited to meet this growth, and as result, desalted seawater in Kuwait became the main source of potable water, about 93% in 2002. The electric power and desalted water, produced in co-generation power desalting plants (CPDP), consumptions are continuously increasing, almost doubled every 10 years, due to population and standard of living increases. This led to the consumption of huge amounts of fuel, draining the country main fuel (and income) resource, and negatively affecting the environment. One tenth of Kuwait's oil production was consumed by the CPDP in 2003. If the trend of almost doubling the consumption every 10 years prevails, the total oil production may not be sufficient to desalt seawater for people to drink, and to produce power to run space air conditioning units (a necessity for Kuwaiti harsh weather). It is essential therefore to look for energy efficient ways to produce power and desalted water so as to save the nation's income of these non-renewable fuel resources, to save the environment and indeed life itself in Kuwait, and this is the objective of this paper. It reviews the presently used desalting methods and their energy demand, and the correctness of fuel allocation formulas for CPDP, to determine the most efficient methods to apply and the less efficient ones to avoid. Fourteen desalting cases are analyzed by using the current practice, with and without combination with power generation plants (using steam or gas or combined gas/steam turbines cycles). The specific fuel energy consumed and the emitted CO 2 , SO x , and NO x per m 3 desalted water were calculated for each case. The results show that operating thermally driven desalting systems by steam directly supplied from fuel-fired boilers is the most inefficient practice, and should be avoided. The use of the gas/steam turbine combined cycle, which is also the most efficient power-generation cycle, to drive seawater reverse osmosis (SWRO) desalination plants is the most efficient combination. Also, all conservation measures in utilization of both water and power should be applied. Reclamation of waste water, at least for non-potable water needs must be promoted, because it consumes less energy and at cost much lower than those of desalting seawater.

Gulf countries, experienced very rapid growth in th e last four decades by the evolution of oil production and its price increase. The main source of portable water, about 93%, was secured by desalting seawater in 2002. The inc rease of the daily-consumed fresh water in liters per capita (from 137 in 1973 to alm ost 500 in 2003) and population increase (from 900,000 in 1983 to more than 2,540,0 00 in 2003) necessitate the production of large quantities in desalted water wi th huge amounts of consumed fuel energy. Thermally operated desalting units usually obtain their thermal energy input by steam supply; either extracted from steam turbin es or from heat recovery steam generators HRSG combined with gas turbines. Therefore, most desalted water is produced in cogeneration power desalting plants CPDP. The effect of fuel consumed for desalting seawater on environment is underestim ated by desalination expertise by thinking that, "thermal desalination associated to power generation plant will only be minimally responsible for the discharge of the flue gases to the atmosphere as this impact can be associated to the power generation." However, 21% of the fuel consumed in Kuwait CPDP in 2003 was used for desalting the water. Burning fuel to desalt water increases the environment pollution by producing the carbon dioxide CO 2, the nitrogen oxides NOx, and sulfuric oxides SOx, w ith quantities directly related with the consumed fuel energy for each desalting process . As the efficiency in both power and desalting water increase, the impact on the env ironment decreases. The consumed electric power and desalted water are almost double d every 10 years. If the oil production, (Kuwait main source of income) is 2 mil lion barrels per day, then one tenth of this oil production was consumed by power and water productions in 2003, consequently, 20% and 40% of Kuwait oil production (or total income) will be consumed by water and power productions only in 2013 and 2023 respectively. In about thirty years, the total oil production may no t be enough for people to drink and live in air-conditioned space in Kuwait. The aim of this paper is to look for energy efficie nt ways to desalt water and produce power to save the nation's income, non-renewable fuel resources, environment, and the life itself in Kuwait. It is equally important promote the conservation measures for both the water and power.

This paper presents the status of water desalination in Kuwait, and the limitations of current equipment in satisfying the increased water demand. It also gives the reasons for the water problem, and presents a more efficient and rapidly deployable solution for power and desalinated production. Kuwait has a serious water problem that can become a real crisis in the near future. The country's only natural water resource is 60 m3/y per capita of renewable water wells; while well extraction is 307 m3/y per capita [1]. The absolute and normal water poverty lines are defined by 200 and 1000 m3/y per capita respectively. Desalinated seawater is the main water resource for potable water, beside low salinity brackish well water (≈7% of potable water). In 2002, the average daily water production (and consumption) were: 248 million imperial gallons (MIG) distilled water, 268 MIGD fresh water, and 70 MIGD brackish water [2]. Therefore, desalinated water represents 73.5% of total water resources, and 93% of fresh water. Brackish water is mainly used in agriculture, and for industrial purposes. The water problem is due to many factors. One reason for failure to match the consumed water increase by a comparable desalination capability increase is the lack of steam turbines to combine with multi-stage flash (MSF) units. We recommend introduction of seawater reverse osmosis (SWRO) desalination in addition to MSF. The specific equivalent work consumed by Kuwait MSF units is 22 kWh/m3, while that of the SWRO desalination method is less than 6 kWh/m3. Moreover, SWRO plants take less time than MSF from ordering to hand out.

Kuwait needs to add more desalting units to its present installed capacity to satisfy the growing need of potable water. The energy consumed by different desalting system is one of the main parameters affecting the choice of new desalting system. Every desalting system consumed either thermal, or mechanical energy or both. This paper presents a method to compare these energies on one scale that the equivalent work consumed. Based on this analysis, the energy consumed by the multi stage flash MSF system, the only system presently used in Kuwait to desalt seawater, was calculated and found equal to 25 kWh/m3. This is much higher than the energy consumed by the other two reliable systems, namely reverse osmosis (RO) and multi-effect boiling (MEB) extensively used now in many of the Arabian Gulf Countries, AGC. The average energy consumed by the RO system is 5 kWh/m3, and by the MEB is in the range of 12 kWh/m3 when steam is extracted from steam turbines at low availability.

A numerical investigation was conducted to study the heat and mass transfer between a falling film of calcium chloride desiccant solution and a parallel flow of air in a rectangular fin-tube arrangement. A control volume finite difference method was used to solve the governing equations for the air and the liquid desiccant solution subjected to the appropriate boundary conditions. A model was used to predict temperature distribution on the fin surface. In this model, two approaches were employed to determine the temperature distribution of the fin surface. The first approach utilized the analytical expression for the temperature distribution of a circular fin having the same area as the rectangular fin. The second approach used a finite difference algorithm to directly predict the temperature distribution of the rectangular fin surface. Both approaches were used to study the performance of the fin-tube arrangement for dehumidification of air at various operating conditions. The effects on the air dehumidification process, due to changing the inlet conditions of air and desiccant film; their mass flow rates; and the fin height were predicted. The results were used to developed correlations to predict the heat and mass transfer coeffiecients (on the airside) between the air and the liquid desiccant. These correlations can accurately be used to predict the outlet air and liquid desiccant conditions from the fin-tube arrangement. Correlations were developed to predict the rate of heat and mass transfer between the air and the desiccant film. Several numerical experiments showed agreement with the available data in literature.

Kuwait and most of the Gulf countries, depend mainly on desalted water from the sea for satisfying their fresh water needs. These countries are using the multi-stage flash (MSF) desalting system, as the ‘work horse’ for their water production. This system is less efficient in energy consumption as compared to the reverse osmosis (RO) system. Moreover, large units based on the MSF system have to be combined with steam or gas turbines power plants for better utilization of steam supplied to the MSF units at moderately low temperature and pressure (as compared to steam produced by large steam generators). The value and the cost of the thermal energy supplied to the MSF desalting system depends on the method of supplying this energy. This steam can be supplied directly from a fuel operated boiler or heat recovery steam generator associated with a gas turbine. It can also be supplied from the exhaust of a steam back pressure turbine or bled from condensed extraction steam turbine at a pressure suitable for the desalting process. Any energy comparison should be based on simple criteria, either how much fuel energy is consumed to produce this energy or how much mechanical energy is needed per unit product. The energy consumed in the light of the practice used in most Gulf countries are discussed here. In this study, reference desalting and power plants are used for comparison purposes. This study shows that shifting from MSF desalting system to the RO system can save up to 66% of the fuel energy used to desalt seawater.

The status of power and desalting plants in Kuwait as well as future demands for power and desalted water are outlined. To satisfy future needs, it is planned to connect two multi-stage flash desalting units of 6 mgd each to a steam turbine producing electric power of 300 MW nominal capacity. Steam supplied to the desalting units is usually extracted from the turbine at moderately low pressure after expansion in the turbine. This consumes more energy and needs more expensive equipment compared with RO desalting systems. The use of RO frees the power plants from the connection of its operation with the desalting system. A suggestion for a single-purpose desalting plant with its own power production by gas turbines is presented. Saving of annual fuel consumption with the suggested plan is calculated.

A numerical study has been conducted on laminar natural convection heat transfer in a tilted square enclosure Piled with a fluid-saturated porous medium in the presence of a transverse magnetic field. The vertical walls of the enclosure are maintained at constant temperatures while the horizontal walls are thermally insulated. The flow in the porous region is modeled using Darcy's law and the Boussinesq approximation. The control-volume finite difference method is used to solve the governing equations for different values of Darcy-Rayleigh number, Hartmann number and inclination angle. The numerical results obtained are presented graphically in terms of streamlines and isotherms to illustrate interesting features of the solution. A new correlation for the average Nusselt number is developed in terms of Darcy-Rayleigh number and Hartmann number in vertical cavities. Typical numerical results showed excellent agreement of the present approach with the available data in the literature.

A numerical simulation of two-dimensional laminar natural convection in a fully open tilted square cavity with an isothermally heated back wall is conducted. The remaining two walls of the cavity are adiabatic. Steady-state solutions are presented for Grashof numbers between 102 and 105 and for tilt angles ranging from 60 to 90 (where 90 represents a cavity with the opening facing down). The fluid properties are assumed to be constant except for the density variation with temperature that gives rise to the buoyancy forces, which is treated by the Boussinesq approximation. The fluid concerned is air with Prandtl number fixed at 0.71. The governing equations are expressed in a normalized primitive variables formulation. Numerical predictions of the velocity and temperature fields are obtained using the finite-volume-based power law (SIMPLER: Semi-Implicit Method for Pressure-Linked Equations Revised) algorithm. For a vertical open cavity (alpha = 0 deg), the algorithm generated results that were in good agreement with those previously published. Flow patterns and isotherms are shown in order to give a better understanding of the heat transfer and flow mechanisms inside the cavity. Effects of the controlling parameters-Grashof number and tilt angle-on the heat transfer (average Nusselt number) are presented and analyzed. The results also revealed that the open-cavity Nusselt number approaches the flat-plate solution when either Grashof number or tilt angle increases. In addition, a correlation of the Nusselt number in terms of the Grashof number and tilt angle is developed and presented; a comparison is made with available data from other literature.