HOW THE CRENA MOBILE BIO-SOLID DRYER WORKS
The CRENA mobile dryer is a customized version of the process utilized for the drying of municipal sewerage sludge (Cake) for energy and scaled to handle characteristics unique to livestock manure solids. Specialized components are protected by patents controlled by the company. The components work sequentially to separate and evaporate high volumes of water from waste solid typical to that found in hog manure and collected before disposal. For safety considerations the drying process does not involve the use of pressure vessels or the incineration of solids.
The plant is classified as a Direct Fluid Fired Air Heater that operates at atmospheric pressure with open vented terminals. i.e., there are no dampers or isolating valves between the heating process and atmosphere. The process is arranged to reduce moisture in bio-cake and produce micro-powder which can be burned in suspension as fluid fuel.
The following example emphasizes this claim; If a lump of bio-cake is accepted as having a volume of 500,000 cubic mm (32 cubic inches), and the lump enters the process carrying 75% water (25% solids), the process commences with the evaporation of all moisture thus reducing its volume to 125,000 cubic mm. (8 cubic inches). During this phase the solid mass is broken into 125 million particles at 100 micron with a volume of 125,000 cubic mm and an exposed surface of 7.5 million square mm.
If a comparison is made with oil fired firing in which oil fuel is atomized through a nozzle and fired in suspension, then the exact same situation occurs in a dry micro-fuel firing system where the same size particle is presented to the flame in an exceptionally fine fuel mist. With this situation it can be rightly described that the fuel firing process is ‘fluid in suspension’.
In the process of drying the manure, the drying medium (air) becomes contaminated and must be sterilized, deodorized, and dehumidified before it can be released to atmosphere.
A direct fired air heater receives a mix of fresh air and contaminated air vapour which is raised to a temperature of apx 800oC (1500oF) and it maintained at this temperature for a period in excess of two seconds (as required by international sterilizing standards).
The heated air passes directly into the dual chambered pulverizing mill where it is mixed with collected manure carried into the mill intake from the storage receptacle.
The pulverizing mill reduces the particle size of the solids to increase the surface area as described. As surface area is increased, surface water is evaporated. For purposes of economy moisture in the dry fuel is only reduced to 4%.
The pulverizing mill is designed to process 168 lbs of manure per minute that carries 75% moisture. When dried this volume produces apx 34 lbs of dry powder.
Dry powder is carried from the mill in the air stream and immediately screened and separated to the dry particulate. Evaporated moisture vapor carried in the same air stream is passed on to a dehumidifier which cools the vapor and creates a sterile water condensate.
A portion of the scrubbed air recycles back to the air heater where the carried heat is recovered and mixed with incoming fresh air. The balance is vented to atmosphere.
In circumstances where the dry powder is used as fuel, it provides 100% of the energy for heating which carries out the sterilizing and pathogen removal process. There is no pressurized chamber in the air heater, or the air circulating system. Air pressure throughout the system is maintained at or below ambient by strategically positioned fans that work to draw air through the system keeping internal pressure at or below atmosphere.
The dryer is fitted with dual-fuel burners to facilitate the use of Oil, Gas (propane), or dry fuel operation. In situations where a portion or all of the dried manure is to be used as soil amendment, heating for the airstream is provided by oil or gas or a mixture of both.
If dry fuel is the primary fuel apx 30% of the volume fired is reduced to ash which is collected utilizing a clean in place (CIP) air sweep system built into the floor of the sterilizing chamber. Ash is cooled and collected for other value added applications. .
The CRENA dryer will process any non fibrous bio-solid, including municipal sewage sludge