Tag Archives: Boilers

Smelt-X and Wash-X Services for Chemical Recovery Boilers

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 an explosion when it comes 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 Smelt-X and Wash-X processes which change the way recovery boiler cleaning is executed.


The Smelt-X 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 spouts to lowest point in floor for max 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 and smelt does not touch spouts during the extraction process.  The Smelt-X 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, Smelt-X 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.

The Smelt-X process








Other benefits include:

  • faster cooling – boiler bank and superheater washing can begin sooner
  • recovery of chemicals in the smelt bed
  • minimisation 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
  • safer floor cleaning – reduced need for mechanical cleaning and/or high pressure washing
  • shorter mill shutdown – increase in pulp production



Valmet has also developed a washing service for recovery boilers called Wash-X in which the floor is washed simultaneously with the rest of the boiler using low pressure water sprays and mixing devices installed on the furnace floor.  Once the super heaters are clean, the mixing devices are removed and floor is emptied of wash water using smelt ejectors.

The typical Wash-X arrangement for mixing devices and wash water sprays:

Wash-X arrangement for mixing devices and wash water sprays

  • 1 or 2 mixing devices in each spout (operated with pressurized air)
  • 8 – 18 primary air port sp rays connected to feedwater or warm water system (depending on floor size)
  • black liquor sprays (at least) in front wall (not shown here) spraying warm wash water




The Smelt-X and Wash-X services will save a huge amount of time for companies who need their recovery boiler systems cleaned.  Our process will do no damage to your boiler and have you back operating at full strength much faster than any other process on the market.  Please contact Mike Ward to arrange an in person meeting to discuss how our Smelt-X and Wash-X services can work for you.

Burning NCGs in Recovery Boiler

Utilizing state of the art technology is vital to meeting all of the environmental regulations your mill is subject to both today and in the future. Valmet’s superior system and extremely high oxidation rate can burn off NCG and allow our customers to enjoy an odorless and environmentally-friendly pulp mill. NCG stands for Non-Condensable gases and that they are composed of mostly sulfur gases often referred to as TRS, and gaseous methanol. While at a low concentration they can give off a very strong rotten egg smell, at slightly higher concentrations, they can be toxic.


NCG are collected at various points in the process such as tanks, bins, digesters and washers. They can be in one of two forms: DNCG which are below the flammability limit and will not be able to burn off on their own, and, CNCG which is above the flammability limit where they will need oxygen to burn. Now, in the past mills have used lime kiln, power boilers or a dedicated incinerator to burn off NCG. But there can be problems with these choices. Limekiln burning of NCG can lead to the formation of rings that will cause a loss of production. Burning NCG in a power boiler results in a higher SO2 emissions unless the boiler happens to have a scrubber; there could also be corrosion in the boiler SH and Tubular Air Heater which would cause slagging and plugging issues. The problem with having a dedicated incinerator is that it is both capital intensive and a huge source of maintenance.

The solution to this problem is to turn to the recovery boiler, as it is the ideal location since it is designed to handle black liquor. The SO2 produced is captured by the sodium fumes that are in the boiler and it allows the sulfur to be returned to the pulping process. The heat from the NCG will increase the steam production from the boiler and since the venting of NCG is no longer an acceptable practice, the location of the NCG disposal must be readily available. Recovery boilers are of course readily available as the mill needs to be able to make pulp.

Valmet has extensive experience with the disposal of NCG in the recovery boiler and is able to set up a collection system and have both DNCG and CNCG injected into the recovery boiler is a safe and reliable way.