Alkaline scale abatement

A method of reducing or substantially eliminating alkaline scale formation on evaporative heat transfer surfaces which are in contact with boiling or flashing alkaline brine which contains a substantial amount of carbonate ions formed by decomposition of bicarbonate ions present in said brine, said brine also containing a high-temperature chemical scale control additive selected from the group consisting of polymers and copolymers or maleic acid, polyphosphonates, phosphonic acid derivatives, aminophosphonic acid derivatives, polymethacrylic and polyacrylic acid derivatives, polyolesters, or mixtures thereof, said method comprising the step of dissolving in said brine subsequent to or simultaneously with boiling or flashing thereof an effective amount of carbon dioxide such that the P alkalinity of said brine is maintained at between about 20 and 90 ppm expressed as equivalent calcium carbonate, the pH of the brine is maintained at between about 8.7 and 9.3 as measured at room temperature, and the concentration of chemically uncombined carbon dioxide in said brine is less than about 1 ppm.

In a method of inhibiting alkaline scale formation in brine which is to be evaporated wherein a high-temperature chemical scale control additive which effects threshold scale inhibition is present in said brine during said evaporation, the improvement which comprises the step of adding carbon dioxide to said brine subsequent to or simultaneously with said evaporation in order to lower the P alkalinity and pH of said brine relative to brine treated with said additive alone whereby the scale inhibiting ability of said additive is enhanced, the pH of said brine after carbon dioxide addition being at least about 8.7 as measured at room temperature and the concentration of chemically uncombined carbon dioxide in said brine being less than about 1 ppm.

A method of reducing or substantially eliminating alkaline scale formation on process equipment surfaces which are in contact with evaporating alkaline brine at a temperature of 190.degree. F. or above, which brine contains at least one high-temperature chemical scale control additive which effects threshold alkaline scale inhibition, said method comprising the step of dissolving in said brine subsequent to or simultaneously with evaporation thereof an amount of carbon dioxide sufficient to reduce or substantially eliminate bicarbonate ion decomposition in said brine, yet insufficient to result in substantial amounts of chemically uncombined carbon dioxide in said brine, such that the pH of the brine is maintained at about 8.7 or above as measured at room temperature, and the concentration of chemically uncombined carbon dioxide in the brine is maintained at less than about 1 ppm whereby corrosive conditions and alkaline scale formation are avoided.

A method of reducing or substantially eliminating alkaline scale formation on evaporative heat transfer surfaces which are in contact with alkaline brine at least a portion of which has been heated to a temperature of about 190.degree. F. or above, which brine contains a substantial amount of carbonate ions formed by decomposition of bicarbonate ions present in said brine and a high-temperature chemical scale control additive selected from the group consisting of polymers and copolymers of maleic acid, polyphosphonates, phosphonic acid derivatives, aminophosphonic acid derivatives, polymethacrylic and polyacrylic acid derivatives, polyolesters, or mixtures thereof, said method comprising the step of dissolving in said brine subsequent to or simultaneously with evaporation thereof an amount of carbon dioxide such that the P alkalinity of said brine is maintained a between about 20 and 90 ppm expressed as equivalent calcium carbonate, the pH of the brine is maintained at between about 8.7 and 9.3 as measured at room temperature, and the concentration of chemically uncombined carbon dioxide in said brine is less than about 1 ppm.

In a method of inhibiting alkaline scale formation in brine which contains a substantial amount of carbonate ions formed by decomposition of bicarbonate ions present in said brine wherein a high-temperature chemical scale control additive which effects threshold scale inhibition is present in said brine during said decomposition, the improvement which comprises the step of adding carbon dioxide to said brine subsequent to or simultaneously with said decomposition in order to lower the P alkalinity and pH of said brine relative to brine treated with said additive alone whereby the scale inhibiting ability of said additive is enhanced, such that the pH of said brine after carbon dioxide addition is at least about 8.7 as measured at room temperature and the concentration of chemically uncombined carbon dioxide in said brine is less than about 1 ppm.

A method of reducing or substantially eliminating alkaline scale formation on liquid contact surfaces of a multi-stage evaporator which comprises a series of preceding and succeeding stages, each said stage comprising a brine holding space and a vapor condensing space with a pressure drop between adjacent preceding and succeeding stages wherein alkaline brine flows from each preceding stage to an adjacent succeeding stage, a portion of said brine being evaporated in said succeeding stage, said brine containing at least one high-temperature chemical scale control additive which effects threshold alkaline scale inhibition and a substantial amount of carbonate ion resulting from decomposition of bicarbonate ion in said brine during evaporation, said method comprising the step of dissolving in said brine during evaporation an amount of carbon dioxide sufficient to substantially reduce the rate and extent of bicarbonate ion decomposition in said brine, yet insufficient to result in substantial amounts of chemically uncombined carbon dioxide in said brine, such that the pH of the brine is maintained at about 8.7 or above as measured at room temperature, and the concentration of chemically uncombined carbon dioxide in the brine is maintained at less than about 1 ppm whereby corrosive conditions and alkaline scale formation are avoided.

A method of reducing or substantially eliminating alkaline scale formation on evaporative heat transfer surfaces which are in contact with boiling or flashing alkaline seawater brine at a temperature of 190.degree. F. or above, which brine contains a substantial amount of carbonate ions formed by decomposition of bicarbonate ions present in said brine, said brine also containing a high-temperature chemical scale control additive selected from the group consisting of polymers and copolymers of maleic acid, polyphosphonates, phosphonic acid derivatives, aminophosphonic acid derivatives, polymethacrylic and polyacrylic acid derivatives, polyolesters, or mixtures thereof, said method comprising the step of dissolving in said brine subsequent to or simultaneously with boiling or flashing thereof an effective amount of carbon dioxide such that the P alkalinity of said brine is maintained at between about 20 and 90 ppm expressed as equivalent calcium carbonate, the pH of the brine is maintained at between about 8.7 and 9.3 as measured at room temperature, and the concentration of chemically uncombined carbon dioxide in said brine is less than about 1 ppm, whereby corrosive conditions and alkaline scale formation are avoided.

A method of reducing or substantially eliminating alkaline scale formation on liquid contact surfaces of an evaporator wherein boiling or flashing alkaline brine contains at least one high-temperature chemical scale control additive which effects threshold alkaline scale inhibition and a substantial amount of carbonate ions resulting from decomposition of bicarbonate ions in said brine during evaporation, said method comprising the steps of:

• (a) condensing at least a portion of the water in the vapor stream produced during said boiling or flashing, said stream comprising water vapor, carbon dioxide produced by decomposition of said bicarbonate ions, and other noncondensable gases, so as to enrich the carbon dioxide concentration of said vapor stream;
• and,
• (b) introducing at least a portion of said carbon dioxide-enriched vapor stream to said boiling or flashing brine in an amount sufficient to substantially reduce the rate and extent of bicarbonate ion decomposition in said brine, yet insufficient to result in substantial amounts of chemically uncombined carbon dioxide in said brine, such that the pH of said brine is maintained at about 8.7 or above as measured at room temperature, and the concentration of chemically uncombined carbon dioxide in said brine is maintained at less than about 1 ppm whereby corrosive conditions and alkaline scale formation are avoided.