Recycle of high hardness, high TDS(total dissolved solids) waters (hardness>1000 parts per million (ppm) as CaCO3 and TDS>10,000 ppm) water for steam generation or other reuse such as irrigation or drinking water is very expensive. Silica content is usually above 250 ppm in such waters which can cause problems in steam generation and with desalination. Many of the these high hardness waters are oil field produced waters but there are other processes which generate waters which require additional treatment.For those high hardness waters, hot lime or hot caustic, followed with strong acid/weak acid resin or just weak acid resin softeners are used in conjunction with oil field steam generation. Treatment of these waters for irrigation or drinking waters involves thermal desalination or reverse osmotic(RO) treatment with biological control. Silica removal is not required for normal wet steam genera tion. However for desalination operations, whenever the feed water concentrate is to be used for the steam generator feed and the fresh water sold, silica removal is required to aid in scale formation in desalination plus silica level in the concentrate water. The known limits on the concentrate feed water to a wet steam generator are 500 ppm silica and 25,000 – 30,000 ppm TDS of total water ions, based on soluble salts solubility. Silica removal is also required in other waters such as 210,000 ppm TDS water containing sodium carbonate where silica removal is required prior to crystallization of sodium carbonate crystals. In the softening test work, the high solids addition and disposal associated with a hot lime system was not desired so alternatives were investigated. In addition, better silica removal than silica absorption on magnesium hydroxide or alumina or aluminum was required. Steam stripping of the high pH water and removal of the precipitates using a ceramic crossflow filter for which a special crossflow filter back pulse unit for cleaning was developed. Temperature and pH were increased prior to the steam stripping to decrease steam condensation and drive the reaction. When silica removal was required, a bed of alumina or aluminum was used at the high pH and temperature to put aluminum into solution so aluminum silicates were removed with the hardness precipitates. The solids often contain some oil when using oil field waters so an odor chemical was also developed for the microbiological soil remediation site. The steam stripping was tested first in a countercurrent mode in a stainless steel column clad with a Hastelloy C 22, packed with stainless steel packing. The second test was by injecting the steam on the outside circumference of a crossflow ceramic microfilter in a cocurrent mode with flashing in a exit vessel. In the countercurrent tower operation, the control of the equili brium of the carbon dioxide, the carbonate and bicarbonate at the top of the tower was more difficult than when contacting with the microfilter.With the microfilter, the equilibrium approach was not a large concern as fresh steam was contact ing the water and was then flashed. However the exact control of the steam to water ratio was more difficult in the second case. Both thermal desalination and RO were pilot tested with wa ters from 10,000 to 36,000 ppm TDS to produce potable water with a quartz ultraviolet light for biological (disinfection) control. For wet steam generation, the field produced waters(10,000–24,000 TDS) were tested using strong acid/weak acid resin softening with no silica removal in a 1 MM BTU/Hr wet steam generator.1 The overall operational costs were less than normal sequence of processes mentioned in the literature while the capital costs were in the same range. Patents were obtained on the(1) steam stripping softening, (2)silica removal,(3) back pulse on the micro filter and(4) the odor chemical. A patent on the sour gas treatment is pending.
Generating steam with an oil field water containing high concentration of total dissolved solids (TDS as sum of total ions) and high silica was tested at 1200 psi in the Wilmington Field in Wilmington, California. This work was during 1990 and 1991. Waters with total hardness of 1000-2300 ppm as CaCO3 with 200–300 ppm silica and TDS of 10,000 and 28,000 were treated with conventional strong acid and weak acid softeners. The steam was generated in a small 1 MM Btu/hr steam generator at 75% and 70% steam quality respectively. Besides obtaining operating costs to compare with previous laboratory and field data, this pilot was to confirm on a larger scale, laboratory data that high TDS, high silica waters could be used in steam generation without silicate problems if the hardness and the iron level were controlled to low levels. Our previous experience had indicated that a low iron level was not controlled in most steam generation using recycle produced waters which resulted in silicate problems, sodium iron silicate or acmite. Other softener pretreat systems such as hot lime, caustic, and steam stripping were considered or tested and would need to be considered for a large installation with water of this high hardness. A patent on using steam stripping as a pretreatment has just been issued as the result of associated pilot testing. In water softening, TDS is usually the sum of the cations or anions as CaCO3 but in this paper TDS is the sum of all the ions except sulfides unless otherwise noted. Introduction During the time of water shortage in Southern California, Union Pacific Resources, Inc. had an 80 MW cogeneration unit which used fresh water from L.A. Metropolitan Water District. The steam from this cogeneration was injected into a 2600 foot steam drive at 1200 psi. The formation had previously been waterflood and the reservoir water was about 28,000 TDS. The return steamflood produced water dropped to about 10,000 TDS in about three months and remained relative constant throughout the steam flood. Several options were considered, including tertiary treated sewage water, fresh water from sea water, use of underlying fresh water sands which were downdip of the injection barrier of L.A. Metropolitan Water District, purchasing unused water from other water districts, and recycle of the produced water. All were pursued simultaneous as the economics clearly favored tiny of the fresh water choices. It was estimated that if 10,000 TDS water were injected, the return water TDS would increase, but still be an acceptable alternate. Recycle of produced water has been done by operators in the Bakersfield, Taft and Coalinga area as well as Canada for years. The main Bakersfield area recycle water is fairly fresh water, 2000 TDS, although it can contain high silica. Hagist etc. and Hagist provide good general summary papers on treatment of water for oil field use. In 1967 Hagist reported the injection of 300 ppm silica into a steam generator water and indicated no deposition. There has been numerous cases of silicate deposits in the various recycled waters but most of these can be traced to hardness upsets or high iron levels in the feedwater. Some recycle has also been overseas in steam floods. For example, we participated in the 1986 field tests in Oman, (Rice), where steam was injected at 2200 psi from waters between 5000–14,000 TDS and 1500 ppm hardness as CaCO3. Silica content was low in these waters but soluble iron was high and resulted in some sodium iron silicate evaporator section problems prior to installing iron removal equipment. This water was conditioned by the use of strong and weak acids softeners. Preliminary Resin Tests The resin capacities of both strong acid and weak acid for the various TDS waters are known with in various ranges based on our own previous experience plus the large amount of work published concerning recycle of steamflood and caustic flooding. P. 143^
Pilot tests were conducted on steam flood FWKO process water, oil plus solids from Wemco underdrain and skimmings. The tests were conducted at 70 to 180 F at various pH's. Water wet and oil wet membranes were used to test the various process streams. Ceramic element pore sizes tested ranged from 500 angstroms to 1.2 microns. The FWKO water chemistry and solids content was very variable. It was noted that the microfiltration system performed better (i.e. had higher flux rates and longer run times between cleaning) when a continuous chemical precoat was applied to the membrane. The chemical precoat helped prevent the premature plugging of the membrane pores. Several chemical additives were tested. The pilot tests showed that pH is a factor in the run times achievable on steam flood FWKO process water. The effects of dissolved gases on membrane performance was also investigated. Ceramic membranes are very durable and can be used at high temperatures, and pressures. The membranes can also be cleaned with aggressive solvents, acids and caustics. The membranes have a relatively low flux rate and are expensive when compared to conventional treatment process. They do appear to be useful in the cleanup of concentrated sludge or process water where other conventional filtration does not perform. Introduction This crossflow microfiltration pilot investigation was set up to determine the long-term potential of treating Union Pacific Steamflood Knockout water. More specifically, the pilot was to establish chemical feed rates, flux, and cleaning methods for the ceramic microfiltration system. The pilot system consisted of one P1940 - 500A membrane pilot (CXP-2), and four P1940 - 0.8 elements in series (XP-2). Test Procedures The pilot units were set up to take feedwater from the water leg of Union Pacific Feed Water Knockout (FWKO) vessels 1 and 2. The feed was obtained at vessel temperature and pressure, 160 to 180 F, and 35 psi to 48 psi respectively. The feed hose ran 200 feet, this coupled with the heat loss in the pretreatment tanks, other hoses and membrane housings, resulted in CFM system temperature being 10 F to 20 F lower than the FWKO temperatures. At night, and, especially if it rained, CFM system temperatures would be at or below 130 F, approaching a 50 to 60 F drop in temperature from the FWKO vessels. The initial tests were run with and without the addition of FeCl3. The chemical was added to a pretreatment tank, having a retention time in the order of 15 to 30 minutes, based on the product flow. Total fluid retention time, which includes the recycle, would be 8 to 15 minutes. After March 12, 1991, the system was operated as per the schematic shown in Figure 1. The FWKO was fed into tank 1, where the oil was allowed to skim and/or settle, then through the stripper and into tank 2, where 20–30 mg/L FeCl3 was added, and further skimming of oil occurred. The ferric solids and other precipitates resulting from the stripper were allowed to settle in the bottom of tank 2. CFM feedwater was obtained out of the same suction line for the four 0.8 micron elements in series, as well as for the 500 A unit. The elements were operated until the transmembrane psi pressure differential was 25 to 35 psi, and then the systems were shut down and the elements cleaned. The following data was collected for each unit every 3 minutes during the test runs:Transmembrane differential pressure.Product flow rate.Temperature.pH. P. 137^
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