Productora de Papeles (PROPAL), based in Cali, Colombia, is a group of two paper mills. Originally International Paper operations, they are now owned by the Carvajal family group. Both mills produce paper using sugar cane bagasse as furnish. There are many sugar cane mills in the area, so a year-round supply of raw material is assured.

Commissioned in 1990, today their #2 Mill produces 330 metric tons of paper per day. This paper is used for copier paper, although books and notebooks are also produced with it. Propal has recently purchased a Model VP-24 screw press which will dewater the primary clarifier underflow at this mill.

The project was driven by two factors: environmental and economic. From the environmental standpoint, using the press will eliminate a landfill operation. This landfill can cause run-off and groundwater contamination, besides presenting an ever-growing environmental situation.

Economically the press has a quick payback because the press cake will be dry enough to be combined with their boiler fuel. The press cake has a BTU value of approximately 8,500 BTU per pound of dry matter (compared to 10,000 for coal). Propal’s B&W boilers burn coal. By blending the press cake with this coal, a reduction in coal consumption will result. The use of such biomass fuel has been receiving much attention at paper mills because of increasing energy costs.

The load to be dewatered is 40 metric tons per day (MTPD) of dry solids. It was felt that a Model VP-16 could likely have handled the load. The VP-24 was selected on a conservative basis, anticipating future operating conditions. It is also possible that it may be used to remediate the material in their landfill.

It is noteworthy that the mill already burns 70 MTPD dry solids of chaff and pith that is separated ahead of the digester. This material is pumped to an Andritz belt press where it is dewatered to 40% solids prior to burning.

Propal made use of the Vincent rental fleet. A Model CP-4 press was air freighted to Cali and used for a variety of testing. With this testing it was determined that no pre-thickening or polymer will be required, and press cake with a solids content of 50% can be produced without undue strain or problems. Rent was waived for the test period, and a Vincent engineer assisted at no charge.

The clarifier is an Eimco, 150′ in diameter, handling 9000 gpm. Sand is separated ahead of the clarifier in order to reduce torque loading, and the flow is neutralized. The reject material, mostly medulla or pith, settles to a thick 5% underflow. It is because of this relatively high underflow consistency that no pre-thickening is required.

The original equipment at the WWTP (wastewater treatment plant) consisted of a small Eimco rotary drum screen, followed by a pair of Andritz belt presses. The rotary drum screen is only, approximately, 3′ diameter by 5′ long. This increases the underflow consistency from 5% to 8%. The belt presses, now worn and in need of overhaul, are about 3 meters wide. The cake produced by the belt presses normally has only 15% solids.

The new installation will place the screw press in parallel with the belt presses. That way it will be possible to retain the belt presses, at least for the time being, as back-up. It will also permit the rebuilding of these belt presses. In the future the belt presses may be used to for pond remediation, dewatering sludge from the mill’s treatment lagoons.

The Vincent press was selected over competition because we were able to clearly demonstrate the performance being guaranteed. Because it was an export contract, strong financial assurances were offered in the form of two Letters of Credit. The first L/C, issued by Bank of America to Propal, assures Propal that their down payment money will be refunded should Vincent fail to ship them the press as promised. The second L/C will assure Propal that Bank of America will refund the full purchase price of the press should Propal elect to return the machine. Customer satisfaction is guaranteed.