Well-designed Tree Shredder - EFB single pass dryer – OPPS

SINGLE PASS DRYER SYSTEM

• In single pass dryer, wet furnish is mixed directly with hot gas inside the rotating insulated drum. The wet materials and hot gas normally flow concurrently through the dryer so the hottest gases come in contact with the wettest material.

• The product is dried with hot gas at 350 ºC approx. in the rotary drum. The rotary drum is divided into different sections for a higher efficiency in the execution of the dehydration. In the first contact between the vapor and the product, a spontaneous evaporation is produced resulting in a temperature drop to 150-180 ºC. Immediately after, a slow and progressive drying takes place until reaching a temperature of 95-110 ºC at the outlet of rotary drum.

• The rotation of the drum, with the aid of flights, lifts solids in the dryer so they tumble through the hot gas, promoting better heat and mass transfer. Hot flue gas can be fed directly into the dryer. Other options include using a burner or a steam heater to raise the temperature of incoming air.

• The exhaust gases leaving the dryer may pass through a cyclone, multi-cyclone, baghouse filter, scrubber, ESP or WESP to remove any fine material entrained in the gas. An ID fan is usually placed after the emissions control equipment to reduce erosion of the fan, but may also be placed before the first cyclone to provide the pressure drop through downstream equipment.

1.DRYER DESCRIPTION

Single pass dryer can accept a fairly wide range of particles sizes, moisture content or throughput and still achieve high drying rates. The design permits the use of the highest possible drying temperatures.

The drum rotates by means of two large tracks that lie on four machined rollers, two on each side of the drum. The wheels are mounted on a support block and rotate by means of two bearing supports each one mounted at the end of the wheel shaft. The support block at the rotary drum outlet, has two gear motors which operate the two wheels of that drum block, and thus make the rotary drum rotate on its horizontal ax. Rotation speed of the drum would be adjustable by frequency converter 3-6 rpm. On the drum drive block two position rollers are placed to avoid the longitudinal displacements of the rotary drum, mainly due to expansion. These rollers manage to touch the inside parts of the track, rotating on its shaft when this contact is produced. The rotary drum is thermal isolated by fiber wool and exterior sheeting, thus achieving low radiation heat losses.

The process principle for single pass dryer.

•The technology of our single pass dryer is using Vandenbroek VDB rotary drum dryer. The VDB MPS (Multi-pass-system) is the invention from Vandenbroek, which is used widely in the field of made pallet, biomass, sludge, coal, msw, etc since 1948, and the market share of dryer is around 30% in the world and become one of the most renowned three producers in the market, the other two brands is Nyrup in denmark and Sulzer in Switzerland.

•VDB MPS rotary drum dryer is composite of drum and rotary pass. Every pass has special size of induction plate, and the induction plate is located together with overflow weir plate in the line of shaft as pass. All the induction is combined as block type.
the material is moved in rotary guiding pass by rotary force generated from drum and attractive force from hot air, so that the material can be completely heat exchanged inside the drum, and make sure the final moisture is 2%-3%.

The inner constructure is as follows

Inlet hot air contact with material of high moisture. Heat from high temperature hot air is absorbed by water inside the material and Evaporated. The temperature of material maintenace the same level, the content of water is lowered down by lowering down the temperature of hot air. Later on, the hot air with lower temperature and dried material are going through every pass together, during this process, the remain water inside material is Evaporated in the low temperature.