In 2014, the factory of Refineria del Centro was extended with a new line to produce baker’s yeast. When searching for trustable suppliers, the client favored those making reliable and safe equipment. For the aeration of the fermentation tanks, Sulzer was chosen to provide six completely oil-free HST turbocompressors. This has since been proven to be a winning choice.

The HST turbocompressors are highly efficient, flexible, and deliver 100% clean air. They combine safety and ease of operation.

Marcos Gervan - Yeast Plant Manager, Refineria del Centro
Yeast

The challenge

Baker’s yeast is produced in a multiple-stage fed-batch process. Yeast propagation occurs in successive fermenters operated under aerobic conditions. In the mother and commercial fermenters, the yeast suspension is first introduced and mixed with nourishing media, consisting of molasses and other nutrients, under strong aeration from bottom diffusers.

Once yeast growth starts, the nutrients are fed incrementally which makes the level of liquid rise progressively. Air flow also increases as yeast cells multiply and require more oxygen. At the end of the fermentation, the nutrient feeding stops, and the tanks are progressively emptied and then cleaned and disinfected prior to the next batch. The feed rate of nutrients, temperature, pH, and aeration must be strictly controlled for optimum yeast yield and product quality.

The right aeration is especially critical, as underaeration leads to excessive alcohol formation and overaeration to increased production costs. The air compressors must combine reliability, efficiency, and flexibility to cope with varying flows, which depend on the need for oxygen, and pressure, which depends on the liquid level. Above all, the quality of the compressed air must be perfect in sanitary terms as yeast is a living organism.

Yeast fermentation process
Simplified flowchart

The solution

At Refineria del Centro, the large-scale fermentation is conducted in two large tanks. For each tank, two process cycles can be selected:

  • Cycle 1 - Mother batch: duration of 34 hours, of which 26 hours of growth cycle with continuous air supply, and 8 hours of emptying and cleaning without air supply.
  • Cycle 2 - Commercial batch: duration of 22 hours, of which 16 hours of growth cycle with continuous air supply, and 6 hours of emptying and cleaning without air supply.
The six HSTs in the compressor room
The six HSTs in the compressor room
For both tanks Sulzer tailored the same package of three HST turbocompressors. Each set of compressors is controlled by one Master Control Unit (MCU) to exactly match the changing air needs during the complete cycles. After installation and start-up, the Sulzer technicians continued regular visits on site, providing additional support for the best use of the equipment.
Project data

For each fermenter, with air flow varying from 1’500 to 12’000 Nm3/h and differential pressure from 0.35 to 1 bar:

  • (2) HST20-6000-1-190-40 and (1) HST2500-2-L-4 with a common discharge manifold
  • (1) Master Control Unit (MCU) allowing optimal number of HSTs running in parallel at their best highest efficiencies

In addition to the HST turbocompressors, Sulzer also supplied five AHLSTAR single-stage process pump units for auxiliary applications.

Turbocompressors type HST20-6000-1-190-40

Airflow range 3’000 to 6’000 Nm³/h
Pressure rise 35 to 100 kPa
Input power 190 kW
Power supply 380 – 690 V
Input frequency 50 – 60 Hz
Thermal protection PT100
Max. noise level 62 dBA

Turbocompressors type HST2500-2-L

Airflow range 1’000 to 2’000 Nm³/h
Pressure rise 60 to 100 kPa
Input power 90 kW
Power supply 380 – 690 V
Input frequency 50 – 60 Hz
Thermal protection PT100
Max. noise level 74 dBA
Products
  • HST aeration blower turboblower
    HST™ turbocompressor
    The modern and silent HST™ turbocompressor features an advanced design with proven magnetic bearing technology and a high-speed motor driven through a built-in frequency converter.
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