Flue Gas Desulfurization
Measuring in processes that build up thick layers of gypsum
To remove the corrosive SO2-gas from fossil fuel or waste power plant off gas, a wet scrubber process is used. Limestone, quicklime or calcium hydroxide is used to absorb the SO2 by forming gypsum which can be reused in building materials. Critical in this process is an accurate pH measurement to ensure complete removal of SO2 to meet government standards for clean air.
Power Plants with Flue Gas Scrubber Units
Sector
3 Applications (1. Check pH in Pre-Scrubber, 2. Neutralization, 3. Lime Scrubber)
Application
pH
Measured Parameter
Key Requirements
- The Locations of the measurement points are corrosive and heavy incrustations are formed.
Application Description
Application 1:
In the pre-scrubber (1st stage) the hot flue gas is cooled by injecting milk of lime. The pH value is only slightly increased (typically between pH 1–2 at 80 °C). Here, the pH must not rise above 2 because only HCl / HF and heavy metals are to be precipitated but SO2 binding is to occur at the second stage. Accurate pH control is essential.
Application 2:
In the second stage, the main scrubber, the pH is increased by further addition of lime. SO2 is bound. Here, the lime milk addition must be controlled by continuous pH measurement. When the pH values are too high, too much lime has been added (increased costs) and the gypsum is polluted by excess calcium hydroxide. When the pH values are too low, the binding of SO2 is less efficient.
The optimum lies between pH 5.5 and 6.0. Higher values lead to soft and greasy calcium sulfite coatings (soft plugging) at slightly reduced efficiency. Lower pH values cause heavy incrustations which are difficult to remove (hard scale formation). Generally, the pH measuring point lies in the backflow circulation line of the calcium sulfite / gypsum sludge.
Application 3:
The excess water remaining after precipitation / thickening of the gypsum must be subjected to a neutralization procedure. For that purpose, sulfuric acid is added to bind the excess lime. Also, at this measuring point, there are heavy incrustations and deposits.
All 3 measuring points are extremely important to run the process in optimal condition. The locations are corrosive and heavy incrustations are formed, resulting in high maintenance. Knick recommends fully automated cleaning and calibration systems for these applications to reduce manual labor and increase process safety.
Requirements of Application
The immense challenge of this application is building up thick layers of gypsum in the gas scrubber units.
Why Knick ?
Ceramat is the only fitting which can be used due to the unique ceramic sealing. Deposit remover (“Pump Sock”) for Ceramat can remove deposits, which would otherwise clog the system completely. The unique Sensor Maintenance System cleans and calibrates the sensor fully automatically and reduces the maintenance efforts tremendously.
Solution - Product Highlight
Features
- High resolution graphic display
- Carbon steel or stainless steel housing
- 4 wire, ex zone
- Full diagnostics
- status messages according to NAMUR
Customer Benefit
- Various input and output connections for integration into process
- Flexible due to various modules for measuring and communication
Features
- Up to 130 °C, up to 10 bar
- 2x open hole
- Solid polymer
- For heavy industrial application with a lot of impurities and precipitations
- Memosens technology
Customer Benefit
- Long lifetime even in harsh conditions
- Remote calibration
- Sensor/cable connection can be submerged in water (Memosens)
Features
- Automatic cleaning and calibration of pH measuring point
- Timer or remote controlled
- Available in ex zone
- Easy installation and operation
Customer Benefit
- All 5 media (air, water, cleaning and calibration solutions) are connected in one tubing and by one connector plug
- Local switch for maintenance
Features
- Ceramic parts for long life in corrosiveand abrasive suspensions
- No gaskets, lowest maintenance
- Available in ex zone
Customer Benefit
- Lowest maintenance
- Long service life
- Effective cleaning and protection of sensor