Flue Gas Desulfurization

Download (313 KB)

Reducing Slurry Noise for Stable and Accurate Measurements

Plant Name:  Power Plant
Industry:        Chemical
Product(s):    Power Process


In order to reduce emissions of air pollutants such as sulfur oxides (SOx) and nitrogen oxides (NOx), power plants have installed flue gas desulfurization systems known as scrubbers.

Flue Gas Desulfurization

Figure 1: Flue Gas Desulfurization


Wet flue gas desulfurization or scrubber systems are very effective in reducing sulfur dioxide (SO2) emissions caused by coal combustion boilers. The flue gas discharged from the boiler is fed into the absorber, where a mixture of water and pulverized limestone is sprayed on the flue gas. The limestone slurry reduces sulfur emissions by absorbing the SO2 contained in the flue gas. The limestone reacts with SO2 to produce calcium sulfite. The calcium sulfite then reacts with oxygen and is finally removed as gypsum.

Magnetic flowmeters are typically used to measure the flow of the limestone slurry to the sprayers. A key issue is that the limestone and gypsum slurries are very abrasive. In this application, a conventional, polytetrafluoroethylene (PTFE) lined magnetic flowmeter has a short life expectancy. Non-retained liners and electrodes that expose their seals to the slurry can cause meters to fail. Once the liner wears away or the seal around the electrode is eroded, the process fluid can damage internal components such as coils and electrode wiring.

In addition, electrodes that protrude into the process can increase signal noise as the limestone or gypsum solid particles collide with them. Since conventional electronics cannot distinguish the noise from the flow signal, the resulting erratic output from the meter is unsuitable for control.

Incorrect installation can also cause metering problems. In addition to the typical installation requirements in terms of lengths of upstream and downstream straight pipe runs, maintaining the velocity of the slurry within certain limits is very important. If the flow rate is below 1.5 m/sec (5 ft/sec), the limestone can fall out of suspension. In a horizontal pipe, this can subject the bottom of the meter to excessive wear. If the flow rate is greater than 2 m/sec (7 ft/sec), the limestone can cause increased wear in the liner. These conditions can significantly decrease the life of the meter.


Yokogawa has designed the ADMAG Total Insight, AXG magnetic flowmeters for this application. As shown in Figure 2, retained liners and insertion style electrodes isolate the sealing surface from the process fluid and increase service life. The flush electrode reduces the potential for slurry noise. In addition, ADMAG's dual-frequency excitation and the optional, enhanced dual-frequency module will provide more stable and accurate measurement than comparable flowmeters.

Figure 2 - Retained liners and insertion style electrodes remove sealing surface from process fluid for enhanced service life


Figure 2 - Retained liners and insertion style electrodes remove sealing surface from process fluid for enhanced service life


For limestone slurry flow measurement, best practice is flow in an upward direction through a vertical pipe at a velocity between 1.5 to 3 m/sec (5 to 10 ft/sec). This keeps the limestone suspended in the water and minimizes liner wear. A metal hat “earth ring” can also reduce erosion by protecting the leading edge of the liner.

When these installation recommendations cannot be met, a ceramic-lined meter should be considered. The ADMAG ceramic meter would be well suited to such applications due to the abrasion resistance of its liner and to the flush and fused platinum electrode, which reduces slurry noise. Furthermore, the ADMAG CA, capacitance type magnetic flowmeter, which is ceramic lined and has no wetted electrodes, offers a solution for abrasion resistance and immunity to slurry noise.

Key Advantages


  • Dual-frequency excitation provides fast response time, zero stability, and noise reduction to enable precise control.
  • Retained liners and insertion style electrodes extend service life, minimize OPEX and long-term total cost of ownership (TCO).
  • PFA and ceramic liners significantly reduce meter failures and downtime in harsh conditions such as slurry flow measurement.


  • Chemical

    Chemical plants rely on continuous and batch production processes, each posing different requirements for a control system. A continuous process calls for a robust and stable control system that will not fail and cause the shutdown of a production line, whereas the emphasis with a batch process is on having a control system that allows great flexibility in making adjustments to formulas, procedures, and the like. Both kinds of systems need to be managed in available quality history of product, and to be able to execute non-routine operations. With its extensive product portfolio, experienced systems engineers, and global sales and service network, Yokogawa has a solution for every plant process.

    See More
  • Oil & Gas Downstream

    The oil & gas downstream industry has been facing an increasing number of challenges in recent years. These include the changing characteristics of the feedstock to be processed, aging of process facilities and equipment, rising cost of energy, lack of skilled plant operators who can run a refinery safely and efficiently, and the ever-changing requirements from both the market and the customer.

    Over the years, Yokogawa has partnered with many downstream companies to provide industrial solutions focused on solving these challenges and problems. Yokogawa's VigilantPlant solutions have helped plant owners to achieve maximum profitability and sustainable safety within their plants.

    See More
  • Power

    In the mid 1970s, Yokogawa entered the power business with the release of the EBS Electric Control System. Since then, Yokogawa has steadfastly continued with the development of our technologies and capabilities for providing the best services and solutions to our customers worldwide.

    Yokogawa has operated the global power solutions network to play a more active role in the dynamic global power market. This has allowed closer teamwork within Yokogawa, bringing together our global resources and industry know-how. Yokogawa's power industry experts work together to bring each customer the solution that best suits their sophisticated requirements.

    See More
  • Specialty & Fine Chemical

    Yokogawa has long served customers in the specialty and fine chemicals market. With a market leading batch solution that offers the best in class reliability and flexibility as well as industry experts who understand the complex requirements in designing a batch solution, you can be assured that in your partnership with Yokogawa you will have a system that will enable you to produce products that meet your customers’ needs in the future while maintaining safety and regulatory compliance.

    See More
  • Thermal

    Thermal power using coal, oil or gas as fuel accounts for the majority of electric generation throughout the world.

    See More

Related Products & Solutions


    The ADMAG TI series AXG is ideal for industrial applications including oil & gas, chemical, and pulp & paper. With built-in diagnostics and exclusive PFA injection liner, the AXG provides ease of operation while reducing total cost of ownership.

    See More

    ADMAG CA magnetic flow meter is excellent at measurement in ultra-low conductivity fluids down to 0.01 microS/cm, adhesive fluids, or slurry fluids.

    See More
  • Magnetic Flow Meters

    • Magnetic flowmeters ideal for conductive fluids 
    • Chemical, slurry, mining applications
    • Minimal pressure loss
    • Available in 4 or 2 wires
    See More

Have Questions?

Contact a Yokogawa Expert to learn how we can help you solve your challenges.