The DryVac technology provides a cost effective integrated process for dewatering and drying, handling organic and inorganic waste streams equally well. In a single operation involving two stages, the liquid waste is first dewatered and then dried. While the DryVac unit appears physically similar to standard plate filter presses, the actual plates are replaced by DryVac Elastic Envelope Modules (DEEMs) {patent pending}. These modules expand and contract according to pressure being applied either externally or internally.

Stage One: the dewatering takes place in a very similar way as with conventional plate presses. That is, conditioned sludge is pumped into the sludge chambers, which are lined with filter cloths; solids are retained in the press while liquids are forced out.

Stage Two: is where the DryVac process differs from standard plate filtration presses. In the drying stage, low-pressure steam is used to inflate the DEEMs and, at the same time, a vacuum is applied to the filtrate ports. During this process the cake is squeezed as the DEEMs inflate. The application of heat to the filter cake and the pulling of a vacuum on the filter chamber result in the remaining water being vaporized at low temperature. The walls of the expanding DEEMs remain in contact with the sludge ensuring effective heat transfer. By regulating the duration of the drying stage, the dry solids of the end product can be accurately controlled. Because the cake is much drier than with a conventional press, at the end of the drying cycle the solids drop out easier, leaving the DEEMs relatively clean.

The process is energy efficient and it allows wide flexibility of design when retrofitting existing presses. The DryVac systems are available in capacities ranging from 0.06m3 to 20m3 or more. The system is supplied in modular formats for ease of installation allowing maximum flexibility; fully mobile units are also available

Basic Process Layout

The DryVac Dewatering and Drying Process

Feed Cycle Conditioned sludge is fed into the chambers with the feed pump.

Pressure and Air Blow Cycle
Pressurized air is introduced into the chamber to squeeze the cake.
Pressurized air is blown through the cake to remove water.

Drying Cycle
Steam is applied to the steam chamber. Vacuum is drawn on the ‘cake’ via the filtrate ports.

Discharge
Steam and vacuum are turned off and Deems {patent pending} deflate.
Dry product drops out as the press is opened.

SAFE
Automated units are available
Negligible odor emissions
No explosive dust environment
Uses 1 BAR steam (15 PSI)

ENERGY EFFICIENT
Dewatering and thermal vacuum dehydration
Combined effect of pressure, heat and vacuum
Can make use of waste heat
Excellent heat sink for CHP schemes

SIMPLE & FLEXIBLE
Surplus activated, primary or digested materials
Varible Feedstocks including Tank Bottom Materials, Mud, Lime Slurries, PPI and Battery Wastes
Dewaters to 20-40%
Dry Materials to 99%
Low Maintenance
Automated Operation
Skid Mounted if desired
Modular Construction
Retrofits to Existing Presses

· DryVac can compete favorably with, and overcome many of the negatives associated with
   the liming of sewage sludges; the process is virtually odorless.
· From a health and safety viewpoint the process is relatively simple with minimal risk.
· Dried food products can be stabilized and be stored indefinitely.
· The potential to achieve higher dry solids means less cost of transport and disposal.
· Enhanced treatment is achieved.
· Flexibility of disposal options.
· Excellent fit with waste to energy projects.
· Potential for Combined Heat and Power applications with DryVac providing an excellent heat sink.