The starch Jet Cooker is a unique and important process heating device for the production of corn sweeteners and starch grain ethanol. Its primary role is to heat the slurry by injecting high velocity steam into a flowing starch slurry so that the starch granules will gelatinize prior to the liquefaction stage. The Jet Cooker produces a very turbulent steam & slurry mixing zone to insure complete and uniform heating of the starch slurry. The Jet Cooker also has an adjustable pressure drop across the Jet Cooker (Fig. 1) to optimize starch cookout and smooth operation.
The starch cooking system has 3 pressure variables that need to be considered when designing your starch jet cooking system. Each of the pressures below will have a direct impact on system performance and reliability:
- Slurry Pressure into the Jet Cooker – The pressure on the uncooked starch slurry at the inlet of the Jet Cooker.
- Cooked Starch Pressure – The pressure of the cooked starch at the discharge of the Jet cooker.
- Steam pressure – The pressure of the steam at Jet Cooker inlet.
The Jet Cooker utilizes direct steam injection which requires the steam pressure to be higher than the slurry pressure. Stable operation is best when the slurry pressure is less than 50% of the steam pressure. So, the starch slurry pressure at the heater location will determine the minimum steam pressure required. Other factors to consider:
- This variable pressure drop of the Jet cooker makes pump selection very important to stable operation. A progressive cavity pump or centrifugal pump with a flat flow curve is recommended.
- If starch slurry cook temperature is above 212°F (100°C), correct minimum discharge pressure is important to prevent flashing and rough operation.
- Operating at too high of a pressure drop can lead to excessive wear of Jet Cooker components and increased slurry pump energy costs. Some jet cooker designs can only run at a high pressure drop which leads to reliability issues and high energy costs.
As a general rule, the higher the steam pressure used, the larger the safe operating range of slurry pressures that can be used. A wider operating range means less process upsets. There are a number of other items to consider to ensure optimization of your starch cooking system. Contact ProSonix to learn how we can help improve your starch cooking system.