Makeup water treatment is a critical component of the steam generation cycle. It is the means to resupply the system with water suitable for boiler and other operations that, for whatever reason, was lost in the cycle. Unlike other aspects of the steam generation cycle, level control for the water treatment process is not necessarily about efficiency, but rather, accuracy, reliability and safety while providing proper inventory management to ensure chemical storage tanks and makeup water supply meet demand.
The chemical component of the water treatment often presents difficulties for level technologies that may work perfectly on non-chemical applications related to the water treatment process or those with limited variations in the contents of the vessel’s vapor space. Although ammonia, acid, caustic and other chemical storage tanks are not difficult level applications by any stretch, small nuances in how the vessels are monitored relative to level technology can have a dramatic effect on the day-to-day practicality and reliability of the type of instrument(s) used. Additionally, there are safety considerations when replenishing chemicals, as well as short-and long-term maintenance costs, which can be addressed simultaneously with inventory monitoring by implementing a few simple, cost-effective modifications to the instrumentation package.
Considerations for Storage Tank Applications
Demineralization, water header and chemical storage tanks come in a variety of shapes and sizes, usually horizontal or vertical vessels six to ten feet in diameter/height, with the ammonia storage and demineralizer tanks being the largest. It is not uncommon to see some type of level transmitter (ultrasonic being the most prevalent) installed to provide level indication to the control room with a local display at the base of the tank, either in series with the 4–20 mA transmitter output or repeated from the control room. The signal to the control room tracks inventory, acts as a high alarm for overfill protection and establishes the resupply interval. The local display facilitates monitoring the offload of chemicals from the supplier’s truck.
Key Components to Chemical Storage Monitoring
The ideal technology for chemical storage monitoring would be able to address all of these components:
- Inventory Management (for accuracy)
- Resistance to chemical attack (for reliability & maintenance)
- Unaffected by changes in the vapor space of the vessel (for reliability)
- Performance verification (for maintenance)
- Visibility during product transfer (for safety)
Chemical Storage and Water Treatment Level Technologies
Accuracy, reliability and visibility in dynamic vessel environments and operational scenarios are a level technology’s best attributes when addressing chemical storage applications. Any number of level technologies can be used in chemical storage tanks. Adhering to the principles of minimizing the number of variables (e.g., vulnerability to process dynamics, calibration, hardware complexity, etc.) that can affect a technology’s ability to perform as intended is a key step in reducing the total cost of ownership. Guided wave (contact) radar as well as its through-air (non-contact) radar counterpart excel in these areas. These two technologies are also very tolerant to a changing vapor space. Magnetic level indicators (MLI) operating in conjunction with Guided Wave Radar or coupled with a magnetostrictive level transmitter offer redundancy and technology diversity while enhancing visibility for improved safety during resupply operations. There is also the added benefit of redundancy when verifying the primary transmitter’s performance during periodic inspections on scheduled outages or while troubleshooting. When magnetostrictive transmitters are paired with MLIs, they offer an alternative to top-mounted level transmitter technologies while being isolated from vessel contents. For non-chemical or less critical applications in the water treatment process, ultrasonic (non-contact) transmitters are an excellent level measurement solution.
Learn more about instrumentation for every part of the steam generation cycle, from steam drum level control to the condensate recovery process and much more, at steamgen.magnetrol.com.