Using automation to enhance paper mill safety & efficiency
The black liquor recovery boiler is an economic component of the pulping process used in pulp and paper applications to reclaim pulping chemicals. Maintenance of these boilers is considered important, as explosions, failures and incidents caused by fouling buildup in recovery boilers have led to safety risks for employees and lost production time for mills.
Automated technology has been implemented in recent years to better equip millwrights with tools they need to keep employees safe and operations online.
This is a review of the current automated technology solutions available for safe and efficient elimination of fouling associated with black liquor recovery boilers.
Many of these solutions are not confined to recovery boilers and are applicable to many industries outside of the pulp and paper industry.
MPW’s cable crawler is deployed for the cleaning of not only the upper furnace, but also the back pass and under the nose with the capability of reaching tough-to-reach places. The crawler features 2D, high-volume and high-pressure rotating heads that are driven by a servo-motor cable unit. Its ability to be pushed and pulled along the cable allows for focus on critical areas, and the adjustable speeds address tough jobs. The cable crawler can be used in other vertical runs, such as the walls of the boilers. The camera mounted on the crawler gives the operator eyes on the job via a corresponding monitor.
For smelt bed services, MPW offers two options. For boilers that may not have a sloped floor, smelt pumping services are available. The smelt is suctioned from the tank and deposited into a dissolving receptacle.
Also available is the smelt bed wash tool. Hydraulically indexed, 2D with a rotating head, the smelt bed wash tool is directed via a rod with high flexibility.
MPW also has developed single- and multiple-lance machines to conduct automated tube cleaning for gas-over-tube TAH air heater jobs. The SAL-1 (single) and the MAL-3 (multiple) each offer useful cleaning abilities. The SAL-1 is a handheld option, and the MAL-3 can operate up to three lances at once through any kind of tube bundles. Running anywhere from 10 to 40 psi, the hands-free MAL-3 can tackle evaporator or condenser tubes that are horizontal or vertical.
For line cleaning, MPW uses its Auto Box for cleaning green liquor lines. This product is similar to a single-lance machine that is moored to a stand and features a strong air-powered lance that employees control from a safe distance. With the ability to clean up to 1,000 ft of pipe, the Auto Box is used for larger lines. With a back-out preventer, operation of the product is safer for the worker.
Dissolving tanks are crucial to any large-scale cleaning project. Remote crawlers are deployed and offer the cleaning crew versatility. The tanks often contain harmful substances, and the crawlers maneuver in tight spaces to perform some of the dirty work that can be dangerous for humans to conduct.
MPW utilizes two different models of M1-RV remote vacuuming machines. One has a serrated snout that can use fire blast and water nozzle hoses attached to the blast and vacuum. The second has an auger attachment that attacks the difficult-to-extract particles, such as slag and hard soil. The machines can climb stairs, hills or ramps. The worker operates the machines with a joystick and video monitoring.
Efficient Remote Vacuuming
When a Virginia pulp and paper mill accepted bids to clean its white liquor tank, it was looking for a contractor that could conceive and apply a procedure to increase the speed and effectiveness cleaning while removing workers from entering a potentially dangerous setting.
White liquor is a strong alkaline solution consisting mainly of sodium hydroxide and sodium sulfide. It is used in the first stage of the Kraft process for pulp production. Referred to as white liquor due to its opaque color, it is capable of causing corrosive burns and reddening of the skin.
Standard methods of cleaning white liquor tanks include water-blasting the white liquor into a slurry before applying a vacuum hose. Traditionally, a worker would have to enter the tank.
Managers from MPW’s operations teams knew they had access to the trained personnel and equipment to complete the tank cleaning beyond the customer’s efficiency and quality standards. To clean the white liquor tank, MPW used M1-RV remote vacuuming technology.
Custom-designed and fabricated by MPW engineers, the M1-RV is an automated vacuuming system. The tool increases cleaning efficiencies and eliminates the need for technicians to enter potentially dangerous confined space areas. The vacuum, in conjunction with a high-pressure water nozzle and an auger, fractures solid debris for easy removal. Using a video monitor, technicians aim the spray and adjust the nozzle with a mechanism that works similarly to a joystick.
The M1-RV was a success, completing the tank cleanse without the need for water blasting. The avoidance of human entry into the white liquor tank was the most important aspect of the project. The M1-RV was unfazed when a chunk of the white liquor broke loose and fell onto the robotic base. Workers present said the incident would have led to an injury if a worker had been in the tank at the time.
MPW completed the project one week faster than previous contractors, allowing for early inspections and returning the equipment to online status sooner than planned. This efficiency saved the customer approximately $40,000. Success on this project has helped MPW secure an expanded role at this location. There were no safety incidents encountered during this project.
The client awarded MPW with perfect ratings on all eight key performance indicators on a job performance evaluation. A department manager wrote: “New technology was very much an asset on this job! Work came in ahead of plan and below cost.”
- Benefits of remote vacuuming include:
- Eliminating the need for technicians to enter dangerous areas;
- Simultaneous cleaning and vacuuming with auger and blast nozzles;
- Easy set up and operation by one technician;
- Increased cleaning quality results in shorter outages;
- Better mobility with the robotic base;
- Easy ascent and descent of stairs and ramps; and
- Increases cleaning efficiency.
While working in hazardous environments, robotic tools can assist with:
- Decreasing safety- and quality-related incidents;
- Eliminating the need for workers to enter potentially dangerous spaces by offering hands-free operation;
- Pinpointing exact locations of obstructions and defects through the utilization of cameras; and
- Increasing efficiency, decreasing downtime and providing detailed and consistent monitoring