Energy recovery EU−Project LIFE04 env ⁄ d ⁄ 000051

• Energy recovery and environmental benefits

  During the production process, vapors with a temperature of approximately 95°C are generated while drying and conditioning the seed. The idea was to develop a method to re−capture this
  energy and re−use it in the production process.
  Sponsored by the EU−project LIFE04 env ⁄ d ⁄ 000051, and together with Bulkflow Technologies Inc,
  a company specialized in heat transfer technologies for solids, an innovative process was developed.

• An energy recovery system

  An energy recovery system was designed, in which the hot vapors leaving the dryer are contacted by a closed−loop water stream, thereby capturing waste heat and improving overall thermal efficiency. The heated water is then used to pre−heat the rape−seed entering the process through the use of a special Rape Seed Pre−Heater developed by Bulkflow Technologies Inc..
  The water sprayed onto the dryer exhaust vapors heats up to a temperature of 70°C. With the use of the Bulkflow heat exchanger, this translates into a temperature gain for the seed of approximately 20°C. The calculated energy savings are significant, representing approximately 90 MM ⁄ MT, which is equivalent to 1.5 MT steam ⁄ hour. In addition to the energy recovery, an important environmental benefit achieved by the waterscrubbing of the hot vapors, is a reduction in odors from the system.
  Furthermore, the higher temperature of the rape seed translates into higher efficiency processing parameters, which is beneficial to the entire production process.

• Bulkflow™ Plate Heat Exchanger Technology

  The Bulkflow™ Plate Heat Exchanger operates by combining mass flow of bulk solids with conventional, indirect heat exchanger technology. This technology was implemented at the rape seed processing facility of Cargill GmbH in Mainz. Instead of using air, the exchanger uses hot water, passing counter−current to the product flow, through welded, hollow, stainless steel plates. The Rape Seed passes slowly by gravity between the plates, in mass flow, thereby heated up to a uniform temperature. Below the Plate Bank, a Mass Flow Cone and Rotary Valve controls the flow of bulk solids through the exchanger.
  The vertical configuration provides for a large heat transfer area in a compact unit, making for a very efficient design. This indirect method of heat transfer eliminates emissions and the need for fans, scrubbers or other costly air−handling equipment.

• Mass Flow of Bulk Solids

  
  Mass flow is an important and critical element in the successful design of a Bulkflow™ Heat Exchanger. To achieve uniform heating, the product must move with uniform velocity over the full cross section of the cooler. To achieve mass flow, a custom designed discharge device is fitted at the outlet of the unit, which ensures uniform draw−down of the product through the exchanger. At the top of the Bulkflow Heat Exchanger, an inlet hopper ensures good distribution of the product to the heat exchanger plates.

  «« Mass flow of bulk - solids between water and cooled plates

• Indirect Heat Exchange by Conduction

  Instead of large quantities of air, the Bulkflow Heat Exchanger uses hot water flowing through fully welded stainless steel plates which are in direct contact with the Rape Seed.
  The heat transfer fluid, flows counter−currently to the product to gain greater thermal efficiency. The dominant heat transfer mechanism is by conduction.
  This indirect method of heat transfer eliminates emissions and the need for fans, filters, bag houses or other costly air−handling equipment.
  The vertical configuration of the equipment provides for a large heat transfer area in a compact unit, resulting in a very efficient design.

• The Plate Heat Exchanger

  The Bulkflow Rape Seed Preheater is designed as double bank heat exchanger with a higher thermal efficiency due to offsetting of the plates. This design provides the necessary heat transfer in a single, vertical piece of equipment. The exchanger plates are manufactured from 316L (1.4404) stainless steel, and the casing as well as structural components, from 304L (1.4306) stainless steel. The multiple bank configurations operate with a higher thermal efficiency due to offsetting of the plates.

• Energy Recovery Process
  − Heating Water Loop

  he heating water, produced by direct contact with hot exhaust vapours from the rape seed dryers ⁄ condintioners, is used for heating the rape seed in the Bulkflow Pre Heater in a closed loop system. The heat recovered in this way provides free energy which is used to pre−heat the rape seed using the Bulkflow Exchanger. In addition to achieving energy integration and recovering waste heat this process is also responsible for increasing the overall downstream rape seed flaker efficiency. A reduction of plant odours should also be achievable.

• Operation Experience

  The Bulkflow Preheater was installed at the Cargill plant in Mainz in 2004. It is operated continuously since then. No maintenance was necessary in that time. As shown in the following table a reduction of approximately 20% in steam consumption at the conditioners was demonstrated.
  At regular checking intervals of the Cargill plant no blocking of the plates on the seed and water side was seen, furthermore no corrosion occurred. No odour reduction was seen so far, due to still high temperatures in the stack. The goal is to increase the heat recovery in the stack in order to decrease the temperature of the vapours and thus gain an odour reduction and to preheat the seed to an even higher temperature.

Data evaluation

For a period of 15 days the following data were calculated:

Average of odor measurements, with and without vapor washing:

With this new, innovative method Cargills continuous striving for an environmentally friendly and more cost effective production takes another large step forward.

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