Egg yolk is an excellent source of phospholipids. The user suspends egg yolk powder in ethanol for this purpose. This suspension is filtered and washed several times. The phospholipids obtained in this way are used, for example, as an emulsifier in the chemical industry or in baby food. The filter cake that results from filtration is processed into animal feed.
Previously, the egg yolk powder was resuspended in a series of containers and washed out by means of dilution washing. The user replaced this complex batch process with a continuous process. BHS-Sonthofen analyzed the existing processes and tested alternatives in the laboratory. Ultimately, BHS recommended the use of a belt filter as the most suitable solution.
The indexing belt filter used is a continuously operating, horizontal vacuum filter that makes it possible to separate sedimentation solids gently and reliably. An indexing belt filter of type BF 050-045 B operated with a vacuum pump was installed at the user’s premises. The suspension of egg yolk powder and ethanol is continuously fed into the filtration system. The filter medium is a circulating belt that is moved in cycles. After every cycle stop, the filtrates are individually vacuumed off for each zone. Extracting the phospholipids is a relatively quick process, which means that even a short exposure time can produce significant yield. The multi-stage parallel cake washing setup allowed for highly efficient displacement washing to be achieved.
At this stage, the phospholipids are present in the filtrate. “The continuous process increased the yield of phospholipids by several percent,” notes Detlef Steidl, Senior Director of Sales Filtration Technology at BHS-Sonthofen. It also boosted the efficiency of the washing process: The supplied filter is equipped with three nozzle washers on the filter. “Compared to the previous process using several containers, washing the egg yolk in the belt filter requires significantly less detergent and energy,” Steidl adds. The customer is completely satisfied with the filter’s performance, and the system has also been validated for the production of pharmaceutical substances.
Users dry the filter cake to egg yolk with a residual moisture of 10 percent. BHS developed a suitable continuous drying process and supplied the required 1,700-liter HTK-T continuous dryer. The egg yolk powder that is conveyed from the belt filter to the dryer has a moisture content of 60 to 65 percent. The optimized transfer of moisture in the integrated filtration and drying system enables maximum efficiency in terms of energy consumption, process duration and machine sizes. The dryer delivers a throughput capacity of 485 kg/h.
The filter cake is placed in direct contact with the shaft and the double jacket of the horizontal dryer. Both the shaft and the double jacket are heated with steam. The double jacket is divided into two heating zones in order to ensure gentle heating of the product. The target temperature is between 70 and 80 degrees. A vapor filter passes the evaporated ethanol on to the condensation system. There, the ethanol is collected, so it can be used again in the process.
“The rotating mixer continuously feeds the egg yolk powder through the dryer, so it is discharged with less residual moisture than the ten percent required by the customer,” explains Martin Specht, Sales Manager at BHS. “The blades are arranged in such a way that homogenous mixing takes place and no dead pockets are created.” The dried product is finally discharged into a shaft via a manually adjustable weir. There the powder is crushed and then pneumatically conveyed to a double cooling screw, where it is cooled down to 25 degrees. The final product is then filled into bulk containers for further processing before it is sold as a nutrient-rich basic component for the animal feed industry.