High-quality steam is the key to safe and efficient production in processing plants including refineries, chemical facilities, pulp and paper production, food processing and co-generation plants. Improper chemistry control in the steam cycle can leave your plant at risk for buildup of impurities and corrosion of equipment, insufficient power production, and damages to the environment and plant personnel.
Plant personnel can mitigate these challenges by maintaining boiler and cycle chemistry. A properly designed sampling system, including sample conditioning and on-line instrumentation, is critical to help prevent, recognize and minimize potentially devastating water chemistry events in a facility.
Impact of Steam and Water on Processes
Processing plants such as refineries, chemical plants, pulp and paper mills, and food processing facilities utilize large amounts heat, usually in the form of steam, to operate chemical reactors, distillation columns, steam driers and more. Large amounts of steam heat are also used for district heating, such as for hospitals or university campuses, or municipal heat, such as many buildings in a large city that utilize steam provided by a commercial provider.
There are several types of systems that can generate the steam required for these processes.
Co-Generation SWAS Management
Co-generation power plants generate high-quality steam and electric power for process heating. They require the same level of chemistry control and monitoring as a stand-alone power plant.
Co-generation plants commonly utilize combined cycle plant designs comprised of a gas turbine that generates electricity. Its exhaust is passed through a heat recovery steam generator that generates the steam to power a steam turbine to generate electricity and excess steam to send to process heat exchangers. These plants operate at temperatures of about 650°C (1157°F) and 14-21 Mpa (2000-3000 psig).
The SWAS is critical to providing the insights needed to monitor and control cycle chemistry and ensure system reliability and safety.
Contaminants negatively affect the feedwater systems, boilers and turbines in the plant potentially causing unnecessary downtime and equipment damage. Proper sampling in cogeneration plants has many benefits. Checking the value of Total Organic Carbon (TOC), corrosion-causing materials and scale-causing materials during operation alerts process engineers of an issue. This step confirms the source of the issue and allows the engineers time to remedy the failure and keep the plant running.
Process Boiler Management
Process boilers must be able to operate within the range of 0.7 -3.4 Mpa (100-500 psig) and at approximately 100°C (212°F). Industrial boilers typically require less chemistry monitoring, but controlling boiler chemistry and chemical addition is commonly done automatically by monitoring boiler conductivity and pH. Some systems also monitor condensate for contaminants, as well as makeup water for silica and other contaminants.
Even the smallest industrial boilers used in hot water heating can benefit from monitoring boiler chemistry. A basic single line sample panel is an excellent option for these low-pressure process boilers. This type of panel can help simplify the conditioning of steam, water or non-hazardous process samples. With the addition of cooling water, safe and representative samples can be obtained from individual sampling sites that are remotely located throughout the plant or from a small number of samples in a central location.
Keeping Samples Cool with Sample coolers
Processing plants also use sample coolers to cool a sample from a process stream to maintain safety and the representativeness of the sample. In order to achieve accurate data for steam-cycle chemistry, the Electric Power Research Institute (EPRI), ASTM and ASME recommend cooling water samples to 77°F (25°C) to ensure consistent, accurate test results.
Specific parameter analyzers used in refineries and chemical plants require that the liquid or gas sample be cooled, typically below 122 F (50 C). When selecting the right sample cooler for your facility, it’s important to consider the requirements for each sample line to ensure adequate flow rates and optimize cooling water usage.
Sentry Equipment is a leader in installing and managing SWAS in power plants, and our experts are equipped to help co-generation and other steam and water applications. Learn more by downloading our Heat Exchangers 101 eBook.