Valmet Smelt Extraction service for chemical recovery boilers

Sep 20, 2016

When it comes to cleaning and emptying chemical recovery boilers, Valmet has the services required to do it swiftly and safely. If the recovery boiler cleaning process starts too quickly, the water being used in the washing process may cause damage if it were to come into contact with the molten smelt. In the past, this potential threat has been avoided by waiting 15-35 hours to make sure the smelt bed is frozen and safe to clean. To speed up and improve this procedure, Valmet has developed the Valmet Smelt Extraction and Valmet Recovery Boiler Cleaning processes which change the way recovery boiler cleaning is executed. (The recovery boiler cleaning process has been described in a previous article, available via the Related Links.)

Valmet Smelt Extraction optimizes the smelt extraction processValmet Smelt Extraction

For boilers with decanting furnace floors, smelt extraction is often a routine part of outage maintenance. But truly optimizing the process, both in terms of time required and percentage of smelt extracted, can be a challenging proposition. Our turnkey smelt extraction service exists to alleviate those challenges.

Valmet Smelt Extraction makes use of air ejectors. We insert a 10-20 ft. long stainless steel “straw” with a compressed air line running inside of it down into the lowest part of the boiler. From there, we use mill air or a portable air compressor to create a Venturi effect that entrains the molten smelt and extracts it from the boiler into the dissolving tank. Expensive chemicals are retained and the smelt does not come into contact with the spouts, thus extending their service life. With no moving parts to fail and a depth limit suitable for any boiler we’ve worked on, it offers more thorough smelt removal in less time.

Valmet Smelt Extraction uses air ejectors for more thorough smelt removal in less time

Valmet Smelt Extraction uses air ejectors for more thorough smelt removal in less time.

The Valmet Smelt Extraction process

As part of our smelt extraction package, we arrive on site the day before your boiler shuts down to prep our equipment and help you prepare. We set up our equipment and make sure it works, and sit down with boiler operators and mill management to discuss the outage schedule. If you need assistance getting the boiler in the proper state to burn down the smelt bed to the point where we can perform extraction, we’re more than happy to help implement a proper bed burn down procedure to maximize results by insuring the entire smelt bed is molten. Valmet Smelt Extraction provides the most efficient and thorough means of smelt extraction, allowing our team to help your team minimize boiler outage time.

The outside and inside of the boiler during the Valmet Smelt Extraction process.

The outside and inside of the boiler during the Valmet Smelt Extraction process. For a dynamic view of the process, click on the video in the Related Links section.

The Valmet Smelt Extraction process has been specifically designed to alleviate the recovery boiler cleaning process. The bottom section of the recovery boiler furnace is heated during load reduction so that the whole smelt bed becomes molten, and the smelt is extracted from the floor to the dissolving tank using air-operated ejectors. Our custom designed ejectors for each furnace arrangement are made to extend from the spouts to the lowest point in the floor for maximum extraction. This custom design is unique in the industry, and can’t be matched by our competitors. Our typical extraction time is 1-3 hours.

As stated previously, the Valmet Smelt Extraction process also allows for chemicals in the smelt bed to be recovered and the amount of strongly alkaline waste water is minimized resulting in savings in both make-up and neutralization chemicals. Due to these features, Valmet Smelt Extraction can be carried out safely in the middle of the operation cycle as well, and the operation can continue with the same spouts without any additional risk of spout failures during the rest of the cycle.

Why choose Valmet Smelt Extraction for your smelt removal?

  • Extract a large pool of molten smelt to significantly reduce boiler cool down time and enable maintenance to begin sooner.
  • Remove smelt pool in order to inspect boiler floor tubes.
  • Reduce lost chemicals by recovering smelt pool in dissolving tank.
  • Eliminate risk of damaging floor tubes by using air operated ejectors which have no moving parts – this is more reliable.
  • Ensure spouts troughs are not overheated by not dispensing smelt directly into spouts, especially during water wash cycles.
  • Increase safety by removing the smelt pool before water washing the boiler.
  • Ensure thorough smelt extraction without having to damage/modify hoods.

Other benefits include:

  • safer floor cleaning – reduced need for mechanical cleaning and/or high pressure washing
  • faster cooling – boiler bank and superheater washing can begin sooner
  • recovery of chemicals in the smelt bed
  • minimization of wash water volume and alkalinity
  • savings in makeup chemicals for black liquor
  • savings in neutralization chemicals in waste water plant
  • faster floor cleaning for inspection and repairs
  • shorter mill shutdown – increase in pulp production

For information on safer and effective cleaning of chemical recovery boilers, contact your Valmet representative.