Continuous Fermentation Through Fixed-yeast Fluidized-bed

The new fermentation technology through fixed yeast fluidized-bed is an advanced biological technique in the world of today. Comparing with batch fermentation and /or single concentration continuous fermentation, the new fermentation technology possesses the advantages of quick speed, shout fermentation cycle, high yield, few instruments, and it is easy to realize automation. The production capacity of the new technology is 10 to 20 times as high as that of batch fermentation. In order to develop the technology of refining alcohol from juice of sweet sorghum stem, to reduce equipment investment and to improve economical benefits, Shenyang Agricultural University and Institute of Applied Ecology, Academia Sinica, have jointly engaged in the research work on this new technology. A 286 ml CH-1 type glass reactor, a 2800 ml CH-2 type glass reactor and a SOL CH-3 type stainless steel reactor were designed successively. To observe inner reaction and grasp reaction mechanism, a SOL polymethyl methacrylate reactor was designed. In September, 1989, a 450L reactor and the complete set of technological equipment were designed again. Experimental result showed that the design requirements are satisfied.

Tests show that, since the contact area of fixed-yeast carrier and juice is large, the reaction rate is increased and the fermentation cycle is shorten to be 4 to 5 hours. Because fixed-yeast reproduces unceasingly in the carrier and is not easy to become ageing, the life span of yeast is prolonged, the discharge of organism is reduced, and the environmental pollution is alleviated. Moreover, because the biological reactor is a kink of dumbbell-shaped three-unit vertical equipment, the volume is small, the ground area it occupies is little, and the capital construction investment is greatly decreased. In order to cooperate with the project of "The Energy Integrated Demonstration Base for China's Cold Northeastern Region", technology and equipments of fixed-yeast, which achieves a daily yield of 400 kg alcohol, was designed by the author.

a. Technological Process

The technological process of refining alcohol through fixed-yeast fluidized-bed biological reactor is shown below :

It includes CO2 circulation system, juice flowing and filling system, beer removing system, cooling and warming system, measuring instruments, and particle-producing system.
CO2 circulation system is composed of (along the gas flow) 13 - foam collector, 14 - gas-liquid separator, 15-cooling and purifying tank, 17-gas compressor (No.1), 18-gas-storage bag, 9-gas compressor (No.2), 10-constant pressure gas storage tank, 11 -gas flowmeter, 12-gas chamber.
Juice flowing and filling system consists of 1-juice storage tank, 2 - juice pump, 33-juice filter, 3-high position tank, 4-juice flowmeter, 5 - three-unit fluidized-bed biological reactor.
Beer removing system contains 6-beer storage chamber, 7-solid-liquid separator, 8-beer trough.  37. First column 38. Second column.
An annular pipe is used to sprinkle water for cooling or warming.
Before normal operation of this system, fixed-yeast cells must reproduce. The prepared fixed-yeast particles are filled into the first unit of the reactor. Then, diluted juice of sweet sorghum is introduced into the reactor until it is full. At the same time, aseptic gas should be led in continuously to make fixed-yeast cells to reproduce. This process lasts about 50 hours. When cells reproduce from 106 to 108 per millilitre solution, and the sprouting rate rises from 5-10% to 15-30%, fermentation stage begins.
When normal operation begins, CO2 circulation system and juice flowing and filling system should be started simultaneously. CO2 in the gas bag is pumped into the constant pressure gas storage tank by the No.1 gas compressor. Then, CO2 is led into the gas chamber at the lower end of the biological reactor. Passing through the gas dispersing plank, it eventually enters the reactor and forms the reaction force. Thus, the force makes fixed-yeast particles react inside the third unit of the reactor. At the same time, juice of sweet sorghum inside the high position tank, under the action of pressure, injects into the reactor from two tangentially-mounted spouts in the first unit of the reactor and circulates around the axis. Acted simultaneously by the upward force formed by CO2, juice moves in a upward spiral way. The solid-liquid-gas three-phase flowing layer (shown in Fig.4.3.6) that was formed in the reactor makes the CO2 gas adhered to the surface of fixed-yeast particles be released.
As CO2 gas constantly contacts with fermentation liquid, vigorous reaction state is maintained and the reaction rate is greatly increased. Since juice entered from the tangential spouts in the first until of the reactor, it takes about 5 hours for juice to pass through all of the three units and carry out the reaction. Above 90% of sugar is converted into alcohol and CO2. The eventually formed fermentation beer enters beer storage chamber, and them flows into solid-liquid separator through the outlet. After broken remains of yeast particles have been removed, fermentation beer is introduced to beer storage trough to be distilled.
CO2 gas coming out from the third unit is pumped into CO2, storage bag through beer storage chamber, foam collector, gas-liquid separator and cooling and purifying tank by the compressor. It is prepared to be used next time.

More explanation can be seen on : http://www.fao.org/docrep/t4470E/t4470e07.htm