Impact of interruption of antiscalant dosing or cleaning balls circulation during MSF plant operation

Available safety margins of time and antiscalant dose rate

Brine and scale chemistry in MSF distillers

Scale formation and fouling problems effect on the performance of MSF and RO desalination plants in Saudi Arabia

Evaluation of polyphosphonate antiscalant at a low dose rate in the Al-Jubail Phase II MSF plant, Saudi Arabia

New anti-scalant performance evaluation for MSF technology

High-recovery electrodialysis reversal for the desalination of inland brackish waters

Alkaline scale formation restriction in desalination plants by means of antiscalant additives

Thermal desalination processes involve the heating of seawater to form water vapor which is then condensed to produce salt free water. Multiple Effect Evaporation (ME) and Multiple-Stage Flash distillation (MSF) are the two main processes used for thermal distillation. MSF distillation, currently is the dominant process. MSF distillation is run under pressure at relatively high temperatures (90-125 °C). Scale formation is one of the most critical problems affecting both processes. In the case of MSF, calcium carbonate, magnesium hydroxide and calcium sulfate are the main scale forming salts. The first two scale former salts are usually controlled by keeping neutral the pH of the system by the addition of acid. Scale inhibitors are used to prevent calcium sulfate scale. Because of economical reasons, the trend in the industry is to operate systems at as high a temperature and concentration factor as possible in order to increase purified water production at a lower cost. Safety concerns have also increased the need for acid feed elimination as a mean of controlling pH1. These practices increased the scaling tendencies in MSF processes and created the need for more effective treatment programs to control scale formation on heat exchangers. A new multicomponent inhibitor program that enable operation of MSF systems without the need of acid feed for pH control has been developed. The program prevent scale formation and allows to operate the system under typical or higher concentration factors and temperatures than normally found in MSF evaporators operating with acid feed.

Scale formation and fouling problems and their predicted reflection on the performance of desalination plants in Saudi Arabia

Sustainable performance of NF-SWRO pilot plant with low fouling NF membrane

Bench experiments and laboratory field pilot plant testing have led to the development of a solvent that is selective in removing CO and H S from natural gas at pipeline pressure. The acid gases are physically absorbed in the solvent and no chemical reaction takes place. Introduction A few years ago, most commercial acid-gas removal processes involved the use of either amines or processes involved the use of either amines or potassium carbonate solutions. These materials chemically potassium carbonate solutions. These materials chemically react with hydrogen sulfide and carbon dioxide, giving off appreciable quantities of heat. Heat must be supplied to regenerate the solutions. In recent years, several companies have developed selective solvents to remove acid gases from natural gas and synthesis gas. The selective solvents operate on the principle of pure physical absorption, as one would calculate using vapor-liquid equilibrium ratios (K-values) for the appropriate systems. Since there is a heat of absorption and desorption involved, the heat effects are much smaller than with solutions involving chemical reactions, and the selective solvent can be regenerated without reboiling. Solvent absorption is especially useful in cases where the partial pressure of the acid gas exceeds 150 psia, and preferably 200 psia. The cost advantage of the solvent absorption psia. The cost advantage of the solvent absorption process arises largely from the saving of heat process arises largely from the saving of heat ordinarily used in the regeneration of amines and hot potassium carbonate solutions, which is substantial potassium carbonate solutions, which is substantial when large volumes of acid gas are involved. Preliminary Screening Tests Preliminary Screening Tests Several years ago, we made a detailed study of acid gas processing that led to the discovery of some 11 classes of polar, organic solvents that were effective in removing acid gas. Solubilities of CO and propane were measured in a large number of solvents at 1 atm and about 80 deg. F. Results of these measurements revealed the solvents covered by Union Oil Co. patents. Solubility data related to these solvents and patents. Solubility data related to these solvents and competitive solvents are shown in Table 1. The solubility ratio of CO to propane is a measure of the selectivity of the solvent. A high selectivity is obviously desirable. Some H S solubility data have been included. Table 2 lists properties of these relatively nonvolatile selective solvents. Results from a bench scale pilot plant narrowed the number of solvents of chief interest, and pointed to the need for a field pilot plant for further study. In the fall of 1964, a pilot plant was installed near the Lisbon field, Moab, Utah, to test some of our solvents as well as a competitive solvent on a sour-gas stream; results of the pilot plant tests on methyl cyanoacetate (MCA) and propylene carbonate (PC) are reported here. The pilot plant is still in use to treat fuel gas for gas compressors. Description of Field Pilot Plant The Steams-Roger Corp. of Denver was selected to design and install the field pilot plant, which is shown in Fig. I in a simplified flow diagram. The pilot plant processed up to 1.8 MMcf/D at a pressure of 770 processed up to 1.8 MMcf/D at a pressure of 770 psig during the runs described here. Raw gas psig during the runs described here. Raw gas contained about 30 percent CO and 1 percent H S. Treated gas was obtained with as little as a few tenths of a percent of CO and less than 1/4 grain of H S per 100 scf of gas. The major equipment included in the pilot plant is described below. JPT P. 483

There is clearly a great need to understand the processes of crystallization and solid scale formation that led to the shutdown of 2H evaporator operation at the Savannah River Site (SRS) and could possibly cause similar problems in the future in other evaporators. Waste streams from SRS operations that enter the evaporators generally contain alkaline, sodium nitrate/nitrite-based solutions with various changing concentrations of silicates and aluminates. It has been determined. that the silicates and aluminates served as precursor reactants for forming unwanted minerals during solution evaporation, upon transport, or upon storage. Mineral forms of the Zeolite Linde A group--sodalites and cancrinite--along with gibbsite, have often been identified as contributing to deposit (scale) formation on surfaces of the 2H evaporator as well as to the formation of solid plugs in the gravity drain line and lift line. Meanwhile, solids (amorphous or crystalline minerals) are believed, without direct evidence, to form in the bulk solutions in the evaporator. In addition, the position of deposits in the 2H evaporator suggests that scale formation depends on the interplay of heat and mass transfer, hydrodynamics, and reaction mechanisms and kinetics. The origin of solid scale formation on walls could be due to heterogeneous nucleation and/or to homogeneous nucleation followed by cluster/particle deposition. Preliminary laboratory tests at the Savannah River Technology Center (SRTC) with standing metal coupons seem to support the latter mechanism for initial deposition; that is, the solid particles form in the bulk solution first and then deposit on the metal surfaces. Further buildup of deposits may involve both mechanisms: deposition and crystal growth. Therefore, there may be a direct linkage between the solid particle growth in bulk solution and the scale buildup on the wall surfaces. On the other hand, even if scale formation is due solely to a heterogeneous mechanism, particle growth in the bulk would still affect scale formation by consuming a portion of the scale-forming precursor materials. In either case, solid-particle-formation data must be obtained to understand the problem. Previous and ongoing testing based on the measurement of [Al] and [Si] consumption kinetics have indicated that the format of aluminosilicate may be rapid under evaporator conditions. However, the kinetics of particle formation (both in bulk solution and on surfaces) has not been studied. Conditions that cause extremely rapid particle formation are of particular interest, because in that case the solids-formation reactions in the evaporator would be sensitively dependent on process conditions such as chemical composition, temperature, fluid flow, and heat transfer.

Scale formation and its effect on the performance of once through MSF plant

An operating philosophy to optimise the output, plant life and economy of MSF plants operatin at high temperatures

Current status of materials selection for MSF distillation plants