Case Study – Pulp Roll handling and Storage
A Southern pulp mill produce large rolls and bales of compressed pulp that is used to make fillers, diapers, and other finished products. The rolls range from 20″ to 48″ in diameter and weigh 1,500 to 1,800 pounds. The movement of the rolls from the plant to the finished goods warehouse was accomplished using fork trucks equipped with clamp attachments. The volume of material produced requires a large number of lift trucks and operators in a three shift production mode. The company wanted to explore the possibility of using conveyors or AGV’s (Automated guided vehicles). In addition, the volume of product caused the company to use rail cars for overflow storage. A large volume was shipped by rail and an attempt was made to load the cars so there would be minimum reconfiguring to make a shipment. Demurrage charges were significant.
The project had two major components, storage capacity and material handling.
A cost study was undertaken to determine what additional space was required to provide sufficient storage capacity. Several different configurations of storage were considered. Each of them had differences in terms of depth of storage, access, aisle widths and so forth, and therefore, an impact on total space. Forecasts were developed for a “design year” to determine the future requirements. The analysis included the rail car overflow costs This included demurrage, material handling and material damage. This cost was compared to the cost of new construction and the potential for double handling. Other considerations were qualitative in nature. For example, the added warehouse space would provide for additional dock doors that added flexibility and some efficiencies. The larger warehouse, however, would also create longer travel paths for lift trucks.
Evaluations of the three potential handling methods were prepared. The methods were:
- Lift trucks, base case, as presently in use
- Conveyors to move the loads over long distances in main travel paths
- AGV’s to move loads in cart trains with variable routing
It became evident that the multiple variables created a large matrix of cases to be evaluated. Simulation was cost effective way to evaluate the mix of facility sizes and movement alternatives.
Consideration had to be given to the need to use forklifts to load/unload either conveyors or AGV’s in all cases.
Simulations of the viable alternatives yielded the following:
- An additional 78,000 square feet of warehouse was required. The net cost savings of elimination or rail car storage was sufficient payback on the building investment.
- Neither the conveyor nor the AGV automation provided significant cost savings to offset the capital costs and additional energy cost (for conveyors) that would be incurred to implement them. The need for continued use of lift trucks at either end of the runs, although less than lift trucks only, was insufficient justification.