Reduced blowdown steam generation

Abstract

Steam is generated using high total dissolved solids (TDS) boiler feedwater while still maintaining relatively low boiler blowdown rates. In one embodiment, a boiler is adapted to generate low quality steam from the high TDS feedwater to maintain wet conditions in the boiler tubes to mitigate against fouling/scaling problems. The low quality steam is then separated into a vapor fraction and a liquid blowdown stream. The vapor fraction is superheated to superheated steam. The liquid blowdown stream is allowed to exchange heat with the thus-created superheated steam to vaporize a portion of the blowdown to form a finished steam and a waste stream. This reduces the blowdown to waste and creates more end user steam. The finished steam is routed to its end use, e.g., a hydrocarbon thermal recovery process. Advantages include lower cost, higher efficiency, and less equipment complexity.

What is claimed is: 
     
         1 . A method for generating steam using high total dissolved solids (TDS) boiler feedwater comprising the steps of:
 introducing a high total dissolved solids (TDS) boiler feedwater to a boiler wherein the boiler comprises an evaporator;   generating a low quality steam in the evaporator from the high TDS boiler feedwater;   separating the low quality steam into a vapor fraction and a liquid blowdown stream;   introducing the vapor fraction to a superheater to superheat the vapor fraction into superheated steam; and   allowing the liquid blowdown stream to exchange heat with the superheated steam to vaporize a portion of the blowdown stream to form a finished steam and a waste stream.   
     
     
         2 . The method of  claim 1  wherein the high TDS boiler feedwater comprises from about 3,000 to about 8,000 ppm total dissolved solids including approximately 3,500 ppm TDS, 4,000 ppm TDS, 4,500 ppm TDS, 5,000 ppm TDS, 5,500 ppm TDS, 6,000 ppm TDS, 6,500 ppm TDS, 7,000 ppm TDS, 7,500 ppm TDS and 8,000 ppm TDS. 
     
     
         3 . The method of  claim 1  wherein the low quality steam has a quality from about 60% to about 90% saturated steam including approximately 60%, 65%, 70%, 75%, 80%, 85%, and 90% saturated steam. 
     
     
         4 . The method of  claim 1  wherein the liquid blowdown stream is generated at a high flowrate with high TDS boiler feedwater including a flowrate greater than approximately 15%, 16%, 17%, 18%, 19%, 20%, 21% 22%, 23%, 24% and 25% of the feed rate. 
     
     
         5 . The method of  claim 1  wherein the liquid blowdown stream exchanges heat with the superheated steam to vaporize a portion of the blowdown stream to form the finished steam occurs in a closed heat exchanger, occurs by mixing the superheated steam with the liquid blowdown stream, or a mixing vessel. 
     
     
         6 . The method of  claim 1  wherein the superheater is a separately fired heater from the boiler. 
     
     
         7 . A method for generating steam using high total dissolved solids (TDS) boiler feedwater comprising the steps of:
 introducing the high TDS boiler feedwater to a produced water evaporator wherein evaporator has a mechanical vapor compressor;   generating a low quality steam in the evaporator;   separating the low quality steam into a vapor fraction and a liquid blowdown stream;   transferring the vapor fraction to the mechanical vapor compressor to produce a evaporator distillate;   transferring evaporator distillate to a boiler;   separating a boiler blowdown and a saturated steam;   returning the drum boiler blowdown to the produced water evaporator;   superheating the saturated steam to produce a superheated steam,   allowing the evaporator blowdown stream to exchange heat with the superheated steam to vaporize a portion of the blowdown stream to form a finished steam and a waste stream.   
     
     
         8 . The method of  claim 7  wherein the high TDS boiler feedwater comprises from about 3,000 to about 8,000 ppm total dissolved solids including approximately 3,500 ppm TDS, 4,000 ppm TDS, 4,500 ppm TDS, 5,000 ppm TDS, 5,500 ppm TDS, 6,000 ppm TDS, 6,500 ppm TDS, 7,000 ppm TDS, 7,500 ppm TDS and 8,000 ppm TDS. 
     
     
         9 . The method of  claim 7  wherein the low quality steam has a quality from about 60% to about 90% saturated steam including approximately 60%, 65%, 70%, 75%, 80%, 85%, and 90% saturated steam. 
     
     
         10 . The method of  claim 7  wherein the liquid blowdown stream is generated at a high flowrate with high TDS boiler feedwater including a flowrate greater than approximately 15%, 16%, 17%, 18%, 19%, 20%, 21% 22%, 23%, 24% and 25% of the feed rate. 
     
     
         11 . The method of  claim 7  wherein the liquid blowdown stream exchanges heat with the superheated steam to vaporize a portion of the blowdown stream to form the finished steam occurs in a closed heat exchanger, occurs by mixing the superheated steam with the liquid blowdown stream, or a mixing vessel. 
     
     
         12 . The method of  claim 7  wherein the superheater is a separately fired heater from the boiler. 
     
     
         13 . A method for producing hydrocarbons from a subterranean formation comprising:
 generating steam using high total dissolved solids (TDS) boiler feedwater wherein the steam is generated by:
 introducing a high total dissolved solids (TDS) boiler feedwater to a boiler wherein the boiler comprises an evaporator; 
 generating a low quality steam in the evaporator from the high TDS boiler feedwater; 
 separating the low quality steam into a vapor fraction and a liquid blowdown stream; 
 introducing the vapor fraction to a superheater to superheat the vapor fraction into superheated steam; and 
 allowing the liquid blowdown stream to exchange heat with the superheated steam to vaporize a portion of the blowdown stream to form a finished steam and a waste stream; 
   transferring the finished steam to a hydrocarbon formation, and   producing hydrocarbons from said formation.   
     
     
         14 . The method of  claim 13  wherein the high TDS boiler feedwater comprises from about 3,000 to about 8,000 ppm total dissolved solids including approximately 3,500 ppm TDS, 4,000 ppm TDS, 4,500 ppm TDS, 5,000 ppm TDS, 5,500 ppm TDS, 6,000 ppm TDS, 6,500 ppm TDS, 7,000 ppm TDS, 7,500 ppm TDS and 8,000 ppm TDS. 
     
     
         15 . The method of  claim 13  wherein the low quality steam has a quality from about 60% to about 90% saturated steam including approximately 60%, 65%, 70%, 75%, 80%, 85%, and 90% saturated steam. 
     
     
         16 . The method of  claim 13  wherein the liquid blowdown stream is generated at a high flowrate with high TDS boiler feedwater including a flowrate greater than approximately 15%, 16%, 17%, 18%, 19%, 20%, 21% 22%, 23%, 24% and 25% of the feed rate. 
     
     
         17 . The method of  claim 13  wherein the liquid blowdown stream exchanges heat with the superheated steam to vaporize a portion of the blowdown stream to form the finished steam occurs in a closed heat exchanger, occurs by mixing the superheated steam with the liquid blowdown stream, or a mixing vessel. 
     
     
         18 . The method of  claim 13  wherein the superheater is a separately fired heater from the boiler. 
     
     
         19 . A method for producing hydrocarbons from a subterranean formation comprising:
 generating steam using high total dissolved solids (TDS) boiler feedwater wherein the steam is generated by:
 introducing the high TDS boiler feedwater to a produced water evaporator wherein evaporator has a mechanical vapor compressor; 
 generating a low quality steam in the evaporator; 
 separating the low quality steam into a vapor fraction and a liquid blowdown stream; 
 transferring the vapor fraction to the mechanical vapor compressor to produce a evaporator distillate; 
 transferring evaporator distillate to a boiler; 
 separating a boiler blowdown and a saturated steam; 
 returning the drum boiler blowdown to the produced water evaporator; 
 superheating the saturated steam to produce a superheated steam, 
 allowing the evaporator blowdown stream to exchange heat with the superheated steam to vaporize a portion of the blowdown stream to form a finished steam and a waste stream; 
   transferring the finished steam to a hydrocarbon formation, and   producing hydrocarbons from said formation.   
     
     
         20 . The method of  claim 19  wherein the high TDS boiler feedwater comprises from about 3,000 to about 8,000 ppm total dissolved solids including approximately 3,500 ppm TDS, 4,000 ppm TDS, 4,500 ppm TDS, 5,000 ppm TDS, 5,500 ppm TDS, 6,000 ppm TDS, 6,500 ppm TDS, 7,000 ppm TDS, 7,500 ppm TDS and 8,000 ppm TDS. 
     
     
         21 . The method of  claim 19  wherein the low quality steam has a quality from about 60% to about 90% saturated steam including approximately 60%, 65%, 70%, 75%, 80%, 85%, and 90% saturated steam. 
     
     
         22 . The method of  claim 19  wherein the liquid blowdown stream is generated at a high flowrate with high TDS boiler feedwater including a flowrate greater than approximately 15%, 16%, 17%, 18%, 19%, 20%, 21% 22%, 23%, 24% and 25% of the feed rate. 
     
     
         23 . The method of  claim 19  wherein the liquid blowdown stream exchanges heat with the superheated steam to vaporize a portion of the blowdown stream to form the finished steam occurs in a closed heat exchanger, occurs by mixing the superheated steam with the liquid blowdown stream, or a mixing vessel. 
     
     
         24 . The method of  claim 19  wherein the superheater is a separately fired heater from the boiler.