Proceedings

This paper presents the J-Vap Process, a filter press/vacuum drying technology, including recent advancements in design of the equipment to improve heat transfer efficiency for drying of the filter cake while maintaining the solids loading rates for maximum throughput on municipal wastewater sludge. Early (and some current) versions of this technology used all thermoplastic membrane squeeze filter plates, which have a very low heat transfer coefficient resulting in a prolonging of the drying process. Later advances incorporated a solid metallic heating plate which, while having greater heat transfer, lacked a filtration surface resulting in lower filtration area per m² of equipment footprint, which in turn translates to reduced throughput in the same equipment battery limits.

Typical in-situ filter press drying technology use either a filter pack of all thermoplastic membrane squeeze filter plates or a “mixed pack” design with solid metallic heating plates alternating with membrane squeeze filter plates. In the former non contact hot water is circulated through the envelope space between the membranes and the body of the filter plates for both heating of the filter cake and membrane inflation. This design allows for maximum filtration surface but is inefficient with respect to heat transfer. In the mixed pack design hot water is only circulated through the metallic heating plate providing high heat transfer rates. Individual filtration chambers formed by the plates only have drainage on one side, reducing the effective filter area for the entire machine and affecting throughput by retarding the dewatering process.

The Siemens J-Vap design advances the mixed pack metallic heating plate design to incorporate both high heat transfer rates and dewatering capabilities. The heating plates have an integrated stainless steel heat exchanger plate through which hot water or low pressure steam can be circulated. The heat exchanger plates have been specifically designed to act as a filtrate collection distributor allowing for dewatering to occur on both sides of each filtration chamber maximizing throughput. The stainless steel plates have a heat transfer coefficient that is 175 times higher than thermoplastic membranes. Tests conducted on a laboratory scale and those run at the Moccasin Bend Wastewater facility in Chattanooga, TN on full scale units showed a significant increase in dry solids achieved in the same relative time frame comparing an all polypropylene plate design to a mixed pack design with metal heating plates. Increase in cake solids of as much as 20% were achieved using the metal heating plate vs. the all PP plate pack.  Based on the data, drying efficiencies are increased by 25-30%.  Increases in throughput, based on comparable equipment footprints of non-filtering metallic heating plates, are estimated to be as much as 40% greater.