Heat Exchanger Descaling System Using Blowdown

Abstract

A system for descaling a heat exchanger utilized in a produced water system of a steam-based thermal hydrocarbon recovery operation is provided. The system comprises a heat exchanger for acting on a produced water; a steam separator in fluid communication with a steam generator for separating steam of a steam quality suitable for injection into a hydrocarbon reservoir and blowdown of a lower steam quality, the blowdown being caustic; and a blowdown loop in fluid communication with the steam separator for collecting the caustic blowdown, the blowdown loop also in fluid communication with the heat exchanger for directing the caustic blowdown through the heat exchanger for descaling the heat exchanger.

We claim: 
     
         1 . A system for descaling a heat exchanger in a produced water system of a hydrocarbon production operation using caustic heated water to descale the heat exchanger, the system comprising:
 a) a heat exchanger for acting on a produced water;   b) a caustic heated water supply; steam separator in fluid communication with a steam generator for separating steam of a steam quality suitable for injection into a hydrocarbon reservoir and blowdown of a lower steam quality, the blowdown being caustic;   c) a caustic heated water loop in fluid communication with the caustic heated water supply, the caustic heated water loop loop also in fluid communication with the heat exchanger for directing the caustic heating water through the heat exchanger for descaling the heat exchanger;   d) a valve for controlling the rate of flow of the caustic heated water through the heat exchanger; and   e) a valve for preventing flow of a produced water through the heat exchanger during descaling of the heat exchanger.   
     
     
         2 . The system of  claim 1 , wherein the caustic heated water is blowdown and the system further comprises:
 g) a steam separator in fluid communication with a steam generator for separating steam of a steam quality suitable for injection into a hydrocarbon reservoir and blowdown of a lower steam quality, the blowdown being caustic;   and wherein the caustic heated water loop is a blowdown loop in fluid communication with the steam separator for collecting the caustic blowdown, the blowdown loop also in fluid communication with the heat exchanger for directing the caustic blowdown through the heat exchanger for descaling the heat exchanger.   
     
     
         3 . The system of  claim 1 , wherein the caustic heated water has a pH of at least about 10.5. 
     
     
         4 . The system of  claim 1 , wherein the caustic heated water has a steam quality of 40% or lower. 
     
     
         5 . The system of  claim 1 , wherein the caustic heated water has a saturated liquid temperature of about 310° C. or lower. 
     
     
         6 . The system of  claim 1 , wherein the system comprises a plurality of heat exchangers, each heat exchanger in an isolatable cleaning loop in communication with the caustic heated water loop, thereby allowing individual isolation of one or more heat exchangers with the caustic heated water loop for descaling the one or more isolated heat exchangers. 
     
     
         7 . The system of  claim 2 , wherein the system further comprises a pressure letdown valve for reducing the pressure of the blowdown before inlet to the heat exchanger to ensure the blowdown is at a pressure below an operating maximum of the heat exchanger. 
     
     
         8 . The system of  claim 2 , wherein the system further comprises a blowdown cleaning tank for removing precipitate from the blowdown following descaling of the heat exchanger. 
     
     
         9 . The system of  claim 1 , wherein the caustic heated water loop comprises valving allowing for the blowdown to be passed through the heat exchanger in either a direction of the process flow or in a reverse direction to the process flow. 
     
     
         10 . The system of  claim 2 , wherein the system further comprises:
 a blowdown exchanger in fluid communication with the blowdown loop for removing some heat from the blowdown and producing a secondary caustic blowdown having a lower steam quality than the blowdown generated by the steam separator; and   a secondary blowdown loop in fluid communication with the blowdown exchanger for collecting the secondary caustic blowdown, the secondary blowdown loop also in fluid communication with the one or more heat exchangers for directing the secondary caustic blowdown through the one or more heat exchangers for descaling the one or more heat exchangers.   
     
     
         11 . The system of  claim 10 , wherein the secondary caustic blowdown has a steam quality of 20% or lower. 
     
     
         12 . The system of  claim 10 , wherein the secondary caustic blowdown has a saturated liquid temperature of about 170° C. or lower. 
     
     
         13 . A method of descaling a heat exchanger for use with produced water generated from a hydrocarbon production operation, the method comprising:
 i) generating a caustic heated water from a hydrocarbon production operation;   ii) bringing the heat exchanger offline; and   iii) passing the caustic heated water through the heat exchanger.   
     
     
         14 . The method of  claim 13 , wherein the method further comprises:
 iv) reducing the pressure of the caustic heated water to a level below the operating threshold of the heat exchanger before step iii).   
     
     
         15 . The method of  claim 13 , wherein the caustic heated water is blowdown generated from a steam generator/separator system. 
     
     
         16 . The method of  claim 13 , wherein the caustic heated water has a pH of about 10.5 or higher. 
     
     
         17 . The method of  claim 13 , wherein step iii) is carried out for between about 1 and 12 hours. 
     
     
         18 . The method of  claim 13 , wherein step iii) is carried out for between about 2 and 4 hours. 
     
     
         19 . The method of  claim 13 , wherein step iii) is carried out for about 1 hour.