Smelt Spouts are used to help remove molten smelt from the recovery boiler.

Generally, lower inlet temperatures of the smelt spout cooling water than the minimum recommended temperatures may cause accelerated corrosion due to dissolving tank fumes condensation on the lip of the spouts. This may significantly reduce the lifetime of spouts.

On the other hand, higher outlet temperatures of the smelt spout cooling water than the maximum recommended temperatures may cause steam formation inside the spout (flashing) which will decrease heat transfer significantly causing spout overheating and eventually failing. Most likely due to thermal cracking. It is important that steam does not form in the spout at any given time, as even short term overheating may cause cracking that then propagates through the spout jacket. If a vacuum spout cooling system is used, it is important that the temperatures do not approach boiling point of the water under vac cum, which are lower than under atmospheric or pressurized system.

Smelt spout cooling water flows are also important, as the water is needed to absorb the heat from the smelt. Insufficient cooling water flows result in spout overheating and failure.

Inlet temperature: min 66-68C (150 – 154F) *Andritz
Inlet temperature: min 66C (150F) *B&W

Outlet temperature: max 88C (190F) *B&W

Flow rates: 1.3 - 3.8 l/s (20-60 gpm) *B&W

B&W manufacturers insertable smelt spouts. Follow this link for details.

Bellow is an excerpt from the brochure:

The typical material for spout fabrication is carbon steel plate and tubing. Spouts operate with a minimum of 150F (66C) inlet water temperature to avoid corrosion wastage. Flow rates from 20 to 60 gpm (1.3 to 3.8 l/s), produce an outlet water temperature no greater than 190F (88C) to avoid excessive steam bubble formation in the cooling water jacket. Carbon steel construction has proven to provide maximum thermal fatique resistance, contributing to the formation of a protective frozen layer of smelt on the trough where smelt is flowing. Weld overlay on trough or chromized spouts can be provided to address specific wastage and corrosion problems.

In its Safe Firing of Black Liquor Guidelines, the Black Liquor Recovery Boiler Advisory Committee (BLRBAC) recommends the replacement of spouts every 12 months. With B&W’s special corrosion-resistant features, insurance inspectors at many mills have supported the extension of spout replacement well beyond 12 months based on inspection experience and empirical performance.

Inlet temperature: min 57C (135F) *Andritz
Outlet temperature: max 64-65C (149F) no boiling *Andritz

Loading: 650 tons BL DS /day *VALMET

Dry spouts do not have a water cooling system.

If you have a confirmed smelt spout cooling water leak through the spout water jacket, it is necessary to shut off the cooling water to this spout. Once done, there is a decision to be made:

• Continue Running

If you can run the recovery boiler without this spout, then plug the spout according to the manufacturer's instructions and continue running the recovery boiler. However, be advised that each spout is rated for a specific heat loading. Thus you might have to reduce the load of the boiler in order not to overload the remaining spouts. Additionally, be aware that the heat loading on each spout might not be equal. However, there is a reason why the spout failed. And if this reason is operational, such as improper cooling temperatures (inlet or outlet), improper flows, or improper water treatment and thus deposits inside the spout jacket, then it is likely that with the current operations, other spouts may be close to failure as well.

• Shutdown the Boiler

If you cannot continue running with the plugged spout, shut the boiler down orderly, burning out the bed, and replace the smelt spout.