If you have talked with your plant chemist or chemical provider lately, you are probably aware that prices for many of the chemicals used by generating plants have steadily risen over the past three years (see table). For power plants with evaporative cooling towers, cooling water chemicals have always taken the lion’s share of a typical chemical budget. Boiler and feedwater chemicals are used in very small quantities by comparison.
One utility’s chemical bill. Chemical costs rose sharply between 2005 to 2008. Source: M&M Engineering Associates Inc.
The cost increases are mainly caused by growing overseas industrial production. Other cost increases can be attributed to more transient conditions, such as the recently completed Olympic Games, during which steel and other heavy industry plants were reportedly shut down to improve air quality in and around Beijing.
By the numbers
Sulfuric acid is one chemical whose cost has increased significantly in recent years. Many plants use concentrated sulfuric acid to maintain pH in their cooling water and for regenerating the demineralizer. Sulfuric acid costs jumped 225% since 2005 for one utility, and its experience is almost certainly shared by many others.
Just as with air emissions, domestic production of sulfuric acid in the U.S. dropped precipitously since the early 1990s, while China’s has been increasing. Much of the world’s acid production is closely linked with steel manufacturing. Iron ore smelting is a major source of the sulfur dioxide used to produce sulfuric acid. Sulfuric acid can also be produced by the direct combustion of elemental sulfur, although that process is more expensive.
Concentrated sulfuric acid is used to process phosphate rock into phosphoric acid, which is used to produce fertilizer. Farmers worldwide are dependent on phosphate fertilizers to increase crop yields. It is estimated that 60% of global sulfuric acid production is used for producing phosphate fertilizers. Other major industrial users of sulfuric acid include the refining industry and manufacturers of nylon.
China, which is the second-largest exporter of phosphate rock, recently moved to increase the tariff on phosphate exports, forcing producers to keep more of the phosphate for local use. As a consequence, more of the sulfuric acid production also will be kept for domestic use. Considering the increasing acreage under cultivation for food and fuel in China and worldwide, it is unlikely that the price of sulfuric acid will be coming back down in the near future.
Chemical dependency
In addition to sulfuric acid prices, the prices of chemicals we depend on to prevent calcium carbonate scaling in cooling water and reverse osmosis systems have jumped significantly--and some chemicals have become more difficult to obtain at any price. Many of these anti-scaling chemicals are classified as phosphonates, and, as the name implies, they contain phosphorous.
Three common phosphonates used in cooling tower applications are AMP, HEDP, and PBTC. Though the complete mechanism is not understood, we know that these chemicals disrupt the crystalline structure of calcium carbonate, making it difficult for crystals to grow larger, attach to a surface, and accumulate to the point where they affect heat transfer in the condenser or create visible scale. Using these chemicals allows cooling towers to operate without scaling at higher cycles of concentration than would otherwise be possible.
These chemicals are typically made from yellow phosphorous, which comes from different sources than phosphate rock. However, pricing and demand can push the use of yellow phosphorous away from the production of complex organic phosphonate molecules used in cooling water treatment and toward fertilizer production. Additionally, many of the pesticides applied to crops are organo-phosphorous compounds, which also are manufactured from yellow phosphorous.
Recently, China placed a special tariff of 120% on the export of yellow phosphorous. This cost increase, coupled with increased demand, has caused the price of yellow phosphorous to rise sharply on world markets. In the past year, prices on common cooling tower phosphonates doubled or, in some cases, tripled.
Molybdate (molybdenum) is typically used in closed cooling water applications, though it is also useful at low levels in some open cooling water systems. Metal industry forecasts predict that molybdenum supply deficits are expected to be larger over the next two years. That will surely push already high prices for molybdate even higher in the future.
In sum, you should expect the price of common cooling water treatment chemicals to increase sharply as chemical costs are passed through the manufacturers of specialty chemicals and on to consumers.
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