Supply of eight non-standard decompression panels for the protection of boiler flue gas ducts

supply-of-eight-non-standard-decompression-panels-for-the-protection-of-boiler-flue-gas-ducts

Problem:

  • high operating temperature of the boiler preventing the use of standard decompression panels
  • low duct process pressure of 10 mbar and panel operating pressure of 50 mbar, forcing the application of solutions with high precision of operation
  • the need to protect the system against bursting or deformation as a result of an uncontrolled increase in pressure in the boiler flue gas ducts

Solution:

  • production of eight custom decompression panels with the dimensions of 1020 x 1020 mm, meeting the requirements for the high operation temperature of the boiler as well as the process pressure and operating pressure of the panel
  • a total decompression area of more than 8 m2 for enabling the flue gases to be efficiently vented to the outside in the event of an uncontrolled increase in pressure and ensuring that the Pstat structural strength of the ducts connecting the boilers with the rest of the system is maintained
  • the use of high-temperature sensors to transmit a signal about the activation of protections to the control room after the panels are opened

The manufacturer of fluidised bed boilers asked our specialists to select appropriate safety devices for a system in operation in one of foreign power plants. In order to provide protection against the increase of flue gas pressure in the boiler ducts, it was necessary to choose decompression panels capable of operation in difficult operating conditions.

The nature of the order precludes the use of standard solutions

The standard opening pressure of decompression panels is set at 100 mbar specified for an ambient temperature of 20 or 22°C, depending on the manufacturer. But what if the actual temperature varies by a large margin?

Each panel has a certain actuation precision, the value of which depends on the “know how” of the manufacturer and the quality of workmanship. In the case of high-quality panels, this value is +/- 15%. This means that, under normal conditions, the panel will open when the overpressure is between 85 and 115 mbar. However, the operating tolerance for low‑quality panels can reach +/-50% – such solutions are more sensitive to pressure fluctuations resulting from the normal operation of the system. In the end, this leads to the panels opening too often and, consequently, generating costs associated with unnecessary replacement of the panels.

As we noted above:

  • the standard opening pressure of decompression panels is, on average, 100 mbar,
  • the opening pressure of decompression panels is determined for a specific temperature (usually 20 or 22°C).

How to protect a duct for flue gas from a fluidised bed boiler with a temperature of 400°C? In addition, the process pressure in the duct is 10 mbar and the operating pressure of the panel is set at 50 mbar. All this means that we needed non-standard panels capable of operating at 400°C and characterised by a very high actuation precision.

Protection against uncontrolled pressure build-up in the flue gas ducts

Decompression panels compliant with all of the aforementioned requirements were made following several analyses. This will maintain the Pstat structural strength (50 mbar) of the ducts connecting the boilers with the rest of the system.

The dimensions of the internal flanges of the selected panels are 1020 x 1020 mm, which gives a total decompression area exceeding 8 m2. If an uncontrolled increase in pressure in the duct occurs and the pressure reaches 50 mbar, the panel will open and “vent” the flue gases outside. This will reduce excessive pressure build-up inside the system and thus protect it from bursting or deformation.

In addition to the decompression panels, the supplied solution includes high-temperature sensors transmitting a signal about the activation of protections to the control room after the panels are opened.

Decompression panels as explosion protection

If the decompression panel is used to protect the system against explosion and where flammable dusts or gases can be released to the outside, at least a 2/22 zone must be designated “outside”. In this case, the sensor must be connected / powered by an intrinsically safe battery so that it does not become an additional ignition source when the panels are opened (the same applies to the installation of decompression panel sensors on biomass or coal silos).