Click here to enlarge imageThe cooling system circulates water in an open loop between the process stream and the cooling exchangers. The heat from the process is released to the atmosphere in the form of water vapor at the cooling tower.
The efficiency of the cooling system is critical in anhydrous ammonia production because the process involves heating gasses to 1,400°F and then cooling the product down to -27°F.
Scale buildup in the cooling exchangers dramatically increases the cost of production in three ways. First, diminished efficiency of the cooling system reduces the ammonia production rate. Second, more energy is required to produce ammonia due to inefficient cooling in the unit. Third, manually removing of scale in the cooling exchangers (through pressure washing or acid cleaning) is a difficult and expensive process that requires a shutdown of the entire production process.
The Solution
Jean Sabourin, the chief steam engineer at the RFO complex, turned to GE Infrastructure Water & Process Technologies (W&PT) to analyze the reduced efficiency of the cooling system and to recommend a solution.
“We contract with W&PT as our treatment consultant and chemical supplier for water treatment,” Sabourin said. “We work closely with them, and we expect innovation and improvement not only in the efficiencies of chemical usage, but also in other ways, such as reducing our energy consumption.”
An analysis confirmed that the diminished performance of the heat exchangers was caused by buildup of calcium carbonate scale, a type of precipitation that makes heat transfer less efficient.
After evaluating the possibility of localized chemical cleaning of specific exchanger components, W&PT recommended the application of Ferroquest LP-7202 to the entire cooling circuit. This is a proprietary blend of three organic acids, specifically formulated to remove calcium carbonate scale from cooling systems.
The Results
“Ferroquest LP-7202 has proven very successful in removing scale from the heat exchanger surfaces,” Sabourin said. “In a production run from July through October 2004, we increased our unit production and reduced our natural gas consumption by 114 million cubic feet of natural gas due to increased efficiency of the cooling system. This was equivalent to a reduction of our energy coefficient by 1.3 gigajoules per tonne of ammonia produced.”
During the production run after the introduction of the anti-scale formulation, the efficiency of the cooling system has remained constant, eliminating any production downtime for scale removal.
“We are very pleased with the results,” Sabourin said. “The decreased energy consumption has not only produced a significant cost savings, but it also means that we require less natural gas, a limited natural resource, and we are therefore emitting less carbon dioxide, and nitrogen oxide, which is good for the environment.” [1 tonne = 1.102 U.S. short tons]
