Ghulam M. Mustafa

Nanofiltration as a means of achieving higher TBT of ≥ 120°C in MSF☆

The Saline Water Conversion Corporation, Research and Development Center (SWCC-RDC) carried out exploratory research study to evaluate the adaptability of the brackish water softening nanofiltration technique as a permeation pretreatment of feed to seawater reverse osmosis (SWRO) and as make-up to MSF. This exploratory work was designated as part I of an applied research project that was carried out from March 1997 to May 1998. Based on initial remarkable results, SWCC applied for a patent on the process during 1997. This paper reports on the pretreatment approach and its application to thermal desalination using MSF. The work carried out in part I of this project is reported where make-up to a 20 kiloliter/d MSF pilot plant distiller was either fresh nanofiltration permeate (NFP) or SWRO reject (while SWRO was fed with NFP). This paper also addresses the plan of elevating MSF top brine temperature (TBT) to as high as 160°C since operation at TBT of 120°C with very little or no scale control treatment gave excellent results.

Optimization of hybridized seawater desalination process

Abstract Saline Water Conversion Corporation (SWCC), Research and Development Center (RDC) came up in recent years with a breakthrough in feed treatment to all desalination processes. Selective ions, biomass and suspended solids rejection characteristic of nanofiltration (NF) membranes were utilized to retard the ingress of hardness forming ions and other foulants into desalination downstream processing steps, e.g. SWRO and MSF. NF pretreatment using brackish water hardness removal membranes were applied to seawater pilot, demonstration and eventually commercial desalination plants. A good number of such membranes were tested in order to select the best. The screening scheme revealed couple of interesting facts related to characteristics of various brands and grades of NF membranes. In an earlier stage of this multi phase project these membranes were categorized as groups A, B and C. These groups in the same order were found to give from high hardness and salinity rejection with low flow and product recovery down to low rejection with high flow and recovery. Based on the above findings, it was decided that the most suitable membranes would be those of group B which could give good flow and recovery with reasonable rejections. Membranes of group B were tested at various plant sizes, production schemes and configurations. This paper will concentrate on 4, 8 and 9 inch membrane elements used in NF or NF/SWRO combination to provide make-up to pilot plant MSF of 20 kl/d distiller. Such hybridized production configurations were optimized by testing overall performance. Few prime parameters were closely analyzed to come up with the best combination of NF membrane brand and their operating parameters along with MSF and/or SWRO—MSF hybrid conditions. In the latter case SWRO reject was used as make-up to the MSF pilot plant distiller. Moreover, the testing program locked into further hybridization, whereby MSF heated reject water was used as feed to NF pretreatment section. This was done to establish the effect of feed temperature rise benefits on NF and/or NF—SWRO energy input, yield(s) and product(s) flow and quality. The MSF operation was monitored and its operating results were analyzed. Main components of such analyses were gain output ratio (GOR), fouling factor (FF), top brine temperature (TBT), chemical consumption and product to make-up yield ratio and its quality.

Thermal performance of multi-stage flash distillation plants in Saudi Arabia☆

Abstract The Saline Water Conversion Corporation (SWCC) of Saudi Arabia is currently producing around 16% of the total worldwide capacity of desalted water [1]. The majority of SWCC desalination plants employs the multistage flash (MSF) distillation process which produce 94% of SWCCs total desalinated water. SWCC various MSF distillers are characterized by a wide range of operating and design conditions. The capacity of operating distillers ranges between 2.5 to 7.5 migd. Some large distillers of rated capacity up to 10 migd are under construction in Shoibah and Yanbu. The number of stages of these distillers varies between 16 and 34, while the operating top brine temperature varies between 90°C and 115°C. Design and operating parameters of various SWCC MSF distillers have been collected and effectively utilized to simulate and analyze the thermal performance of these distillers. The thermal performance of each distiller is quantitatively assessed using a computer program which is based on the first and the second law of thermodynamics. A comparative study on energy and exergy analyses is conducted for different MSF plants. This paper also presents a comprehensive micro-thermal analysis to identify the potential for improving plant efficiency. The exergy losses due to irreversibility in different subsystems of each MSF distiller are evaluated. Exergy destruction in the brine heater, heat recovery and heat rejection stages and friction in liquid paths are determined. The impact of different design and operating parameters such as top brine temperature and number of stages on the thermal performance of the MSF system is evaluated.

The performance of different anti-scalants in multi-stage flash distillers

The Saline Water Conversion Corporation (SWCC) of Saudi Arabia is an internationally recognized authority on scale control in multi-stage flash (MSF) distillers. This international recognition came about as a result of many years of work on this topic. There are publications of SWCC on MSF scaling phenomena over the past couple of decades. During the last decade, there was a monumental growth in SWCCs installed MSF plant capacities. The majority of SWCC MSF distillers were designed to operate with the additive scale control method rather than the previously predominant method of carbonate depletion through chemical reaction with sulfuric or hydrochloric acid. The Research and Development Center (RDC) in Al-Jubail has been involved during the last 3 years in the evaluation of available commercial scale inhibitors. Eight tests have been carried out at the RDC MSF pilot plant, Jeddah Phases III and IV and Al-Jubail Phase II to evaluate the effectiveness of three anti-scalants. These tests by anti-scalant types and places are (1) polycarboxylates in Al-Jubail II, RDC pilot plant and Jeddah IV; (2) polymaleic acid in Jeddah IV and RDC pilot plant; and (3) polyphosphonate in Jeddah III and the RDC pilot plant. This paper presents qualitative and quantitative performance results of three different anti-scalants. The threshold effect of these anti-scalants was tested on laboratory scale. In pilot and commercial plants the variation of the fouling factor with time was examined and quantified. The evaluation tests conducted on the commercial plants revealed that all the examined anti-scalants were successful in inhibiting alkaline scale formation and improving plant performance at a top brine temperature ranging between 105 and 110°C and with respective dosing rates of 1.5 and 3.0 ppm.

Means and merits of higher temperature operation in dual-purpose plants

Abstract For the last 3 years, the SWCC-RDC conducted extensive R&D work on nanofiltration (NF) pretreatment of feed to SWRO and make-up to MSF pilot plants in dihybrid arrangement of NF-SWRO or NF-MSF, also in trihybrid of NF-SWROreject-MSF, where the SWROreject from the dihybrid NF-SWRO is used as make-up to the MSF unit. In both di-trihybrid the MSF unit was operated successfully at 120°C without further acidification, antiscalant or antifoam. The paper summarizes the MSF performance, which was established at operating Top Brine Temperature (TBT) of 120°C, in the dihybrid NF-MSF and trihybrid NF-SWROreject-MSF systems. Because of the excellent MSF performance at this TBT of 120°C, the paper also addresses the planned operation of MSF at elevated TBT of 120 to 160°C and above. These gained advantages in improved performance of MSF when make-up is directly or indirectly from NF (in di- or trihybrid, respectively) triggered a review of dual power and water production cycle of boiler turbine generator: BTG and multistage flash: MSF cycle design. Such combination, i.e., dual purpose BTG-MSF process, could lead to simultaneous increases in water and power production. Simulation model results of such increases are shown in this paper. The described MSF performance also revived interests in gas turbine generator: GTG, heat recovery steam generator: HRSG and steam turbine generator: STG, (with MSF) thus power and water (dual purpose) combined cycle: PWCC.

Simulation of multistage flash desalination process

Abstract The majority of large-scale desalination plants in the Arab Gulf area employ the multistage flash (MSF) processes. MSF processes are energy intensive and it is, therefore, essential to search for design and operating conditions which lead to reduction of energy dissipation and consequently lower water production cost. This paper reports a simulation study which was carried out to examine to what extent the thermal irreversibility of an MSF process is influenced by variation of the most important design and operating parameters. The impact of variation of top brine temperature, number of stages and terminal temperature approach on the distiller performance ratio and irreversibility were explored and presented graphically in the thermal grids. The simulation study revealed that within the selected range of number of stages (16–40) and top brine temperature (90–120°C), the MSF distiller irreversibility is highly influenced by the number of stages and to a lesser extent by the variation of the top brine temperature. The simulated results are compared with one year operating data obtained from an MSF distiller. The distiller is a cross-tube configuration, which consists of 22 stages and operating at a top brine temperature ranging between 90 to 98°C. Using a steady state simulation program, an envelop of possible operating conditions is constructed for the distiller to interrelate performance ratio, production, recycle flow and top brine temperature. Stage-wise simulation of individual heat transfer coefficients and fouling factors showed that both clean overall heat transfer coefficients (Uc) and fouling factors (FF) are stage dependent and conversely the operating overall heat transfer coefficient (UD) is to a great extent less dependent. The dependence of the distiller irreversibility on the process conditions is reported. The distiller energy losses varied between 52 and 62 kJ/kg of distillate. Process details, which are responsible for distiller irreversibility are pinpointed and opportunities for better utilization of available energy are discussed.

Studies on a polyoxypropylene glycol-based antifoaming agent in MSF plants☆

Salt carry-over due to excessive foaming in a multistage flash (MSF) distiller and detrimental foaming in the deaerator section have been reported in the Saline Water Conversion Corporation (SWCC) of Saudi Arabia and other desalination plants. The application of a suitable antifoaming agent has prevented distillate contamination and improved release of dissolved oxygen in the deaerator section, thus improving the operating efficiency of MSF plants. The developer of a polyoxypropylene glycol-based antifoaming agent collaborated with SWCC in carrying out trial runs to show that their product was as effective and economical as the one currently being used (a polyglycol blend in a hydrocarbon solvent) in SWCC plants. Trial tests were carried out at laboratory, pilot and commercial plant levels. Miscibility of this agent in water was determined initially in the laboratory, followed by field trial runs in an MSF pilot plant and the commercial plants of Al-Jubail I and II. Foam control, non-interference with antiscalant performance, distillate purity and stability at a low dose rate over a wide range of temperatures were some of the important criteria evaluated during testing of this antifoaming agent. During MSF plant runs, distillate conductivity and dissolved oxygen level in the feed were regularly monitored and found within the acceptable limits. Compatibility of this agent with antiscalant was also assessed. Heat transfer and plant performance data were found satisfactory confirming that this agent did not exhibit any adverse effect on the antiscalant used in Al-Jubail plants. Results of laboratory and field trial runs of this antifoaming agent are discussed.

Gastrointestinal Basidiobolomycosis Mimicking Colon Cancer in a Sudanese Patient

Basidiobolomycosisis a rare disease caused by the fungus Basidiobolus ranarum. The incidence Rate of Gastrointestinal Basidiobolomycosis is approximately 1 in 45,333,334 or 0.00% in every 5 people in USA), member of the class Zygomycetes found worldwide (1).Basidiobolomycosis is usually a subcutaneous infection but rarely gastrointestinal1. This fungus is found mainly in the soil and on decaying vegetations2. It has been isolated from the banks of tropical rivers in West Africa, and has also been found in association with some insects2. The fungus is known to be present in the gastrointestinal tracts of reptiles, amphibians, and some bat species3. Definitive diagnosis requires culture and serological testing may be helpful. The fungal morphology and the Splendore-Hoeppli phenomenon are characteristic histological features. Basidiobolomycosis is treated with surgical resection and itracanzole 200mg BD for three months or Amphotericin B 5mg /kg iv/24 hrs4. Keywords : Zygomycetes, vegetations, subcutaneous infection.