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Waste Water Treatment Plant Flare Upgrade

A clients Biogas flare was unavailable and unreliable and many attempts were done to try and fix it.

When Bluefield were engaged the flare didn’t run very long and was hard to ignite the pilot. There were a number of issues which resulted the flare to be non-compliant.

 

The original flare stack can be seen in Figure 1

Figure 1 – Original Flare Stack

 

The original nozzle was only 50mm (Figure 2) and had six holes to allow the flow of biogas. This was insufficient so an additional 16 holes were drilled.

 

Figure 2 – Modified Nozzle

 

A new controller (BCU370) was integrated into the existing electrical control panel and then the SCADA system had to be modified to ensure that the flare could be operated remotely. This did require some fault finding and going back to basics as what was installed was not reflected on the drawings.

The pilot system was modified to ensure it was Type B Compliant and a S733 and S697 was issued on completion as per the requirements of the Petroleum and Gas Act.

Once the modification and improvement were made the flare operated when required from Local and Remote stations.  It was found that the flow rates to the flare were 7-8 L/s.

As this flow rate did not meet operational requirements two options were proposed

  1. Replace the existing flare with a new package flare including mechanical, civil, electrical upgrades at a budgetary cost of >$350k with 26-week lead time
  2. Redesign the flare to maximise the existing infrastructure and achieve the maximum flow rate possible at approx. $70k, available within 2 weeks

The decision was made to redesign the flare using existing infrastructure, the maximum flow rate was tested to be 50 L/s with the 75mm pipework.

All the Type B system remained unchanged although a new safety shut down valve was fitted into the Biogas pipework.

The burner nozzle was redesign to have a total open surface area of 75mm. This would allow the maximum flow rate possible as the pipework to the flare was approx. 75mm Figure 3

Figure 3 – New Nozzle

A new flare stack was design to meet the new requirements and built from High Temperature Stainless 253MA. For comparison the old flare stack was Height 750mm Diameter 425mm whereas the new one was Height 1200mm by Diameter 760mm

Figure 4 – New Concept Design

Figure 5 below shows on the right the old flare stack and left new redesign flare stack.

Figure 5 – Old Vs New (Inner Chamber)

The new flare stack was assembled and commissioned and after 12 months was available when called and operated reliable  for the site. Not only has this been a successful project but saved >$280k on a major project.

The maximum flow rate which was achieved for the new flare stack after its redesign has been >42 L/s at times reaching 50L/s (52L/s is maximum). To achieve more output of the flare the existing pipework would have to be upgraded from 75mm to 100mm at a large cost along with all the equipment changes for the bigger pipework.

In its current state the flare is able to reduce the level of the digester tank by 50% in 1 hour.

Figure 6 – Flow Meter

The new flare design can be seen in Figure 7

Figure 7 – New Flare Stack

In addition to the new flare Bluefield carried out

  • A revision of their Hazardous Areas Classification on site
  • Updated the Hazardous Areas Verification Dossier
  • Integrated a new Safety Shut Off Valve into the bio gas
  • Updated their Asset Management system
  • Developed specific Operational and Maintenance manual
  • Developed Work Instruction for correct maintenance operations

Category :

Type B Compliance

Date :

July 16, 2018

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