Direct Steam Injector (DSI)

Direct Steam Injector (DSI) system, commonly used in sterilization processes for liquids. This system heats and sterilizes a liquid medium by directly injecting steam into it, ensuring rapid and efficient heating. Let me explain the process in detail, based on the components in the diagram:

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1. Unsterile Medium In

• The process begins with the unsterile liquid medium entering the system.
• This medium will undergo heating and sterilization in subsequent stages.

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2. Pre-heat Heat Exchanger

• The unsterile liquid first passes through the pre-heat heat exchanger.
• This heat exchanger uses residual heat (usually from the sterilized medium or cooling water) to preheat the liquid before the main heating phase.
• Preheating improves energy efficiency and prepares the liquid for sterilization.

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3. Venturi Valve and Steam Injection

• After preheating, the liquid passes through a Venturi valve, where steam is directly injected into the medium.
• The Venturi effect creates a pressure differential that efficiently mixes the steam with the liquid.
• The steam heats the liquid to the required sterilization temperature almost instantly.

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4. Holding Coil

• After steam injection, the liquid flows through a holding coil.
• The coil provides a specific retention time for the liquid to maintain its sterilization temperature.
• This ensures that harmful microorganisms are effectively killed.

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5. Expansion Chamber and Vacuum System

• The hot liquid then passes through an expansion valve and enters the expansion chamber.
• In this chamber, steam is separated from the sterilized liquid.
• Excess steam exits the system via a vacuum outlet, while the liquid is cooled for further use.

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6. Cooling Heat Exchanger

• The sterilized liquid is then passed through a cooling heat exchanger, where it is cooled to the desired temperature.
• Cooling water is circulated in the exchanger to remove heat from the sterilized liquid.
• The cooling water enters and exits through designated ports.

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7. Sterile Medium Out

• The now-sterilized and cooled liquid exits the system as a sterile medium.
• It is ready for safe use in applications like food production, pharmaceuticals, or other sterilized environments.

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Key Features of the Process:

• Rapid Heating and Cooling: Direct steam injection ensures instantaneous heating, while heat exchangers provide efficient cooling.
• Energy Efficiency: Preheating and heat recovery mechanisms minimize energy waste.
• Sterilization: The process achieves high temperatures to ensure microbial destruction.
• Separation: The expansion chamber separates excess steam to ensure proper cooling and maintain sterility.

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This system is widely used in industries where precise, high-temperature sterilization of liquids is required.

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Step-by-Step Procedure

Step 1: Feed the Unsterile Medium

1. Start by feeding the unsterile liquid medium into the system.
2. The medium enters through the input pipeline labeled "Unsterile medium in."
3. Ensure that the flow rate of the unsterile medium is regulated to match the system's capacity.

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Step 2: Preheating the Medium

1. The liquid flows into the Pre-heat Heat Exchanger.
   • In this stage, residual heat from other parts of the system (like cooling water or sterilized liquid) is used to preheat the incoming medium.
2. This preheating minimizes the energy required for the steam injection process.
3. Monitor the heat exchanger to ensure the preheated liquid reaches the desired pre-sterilization temperature.

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Step 3: Steam Injection for Heating

1. The preheated liquid passes into the Venturi Valve, where steam is directly injected.
2. Open the steam inlet valve to allow high-pressure steam to enter the system.
   • The Venturi valve ensures efficient mixing of steam and liquid.
3. The injected steam raises the temperature of the liquid instantly to sterilization levels (e.g., 121°C or higher, depending on the process requirements).

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Step 4: Sterilization (Holding Phase)

1. The heated liquid moves into the Holding Coil.
2. The liquid is held here for a specific period (retention time), which is crucial to ensure complete sterilization.
   • The retention time is based on the flow rate of the liquid and the length of the holding coil.
3. Monitor the system temperature to ensure it stays above the required sterilization level during this phase.

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Step 5: Steam Expansion and Separation

1. After sterilization, the liquid passes through an Expansion Valve, which reduces its pressure.
2. It then enters the Expansion Chamber, where:
   • Excess steam is separated from the liquid.
   • The steam is vented out through a vacuum system.
3. This step ensures that only the sterilized liquid continues further.

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Step 6: Cooling the Sterilized Medium

1. The sterilized liquid enters the Cooling Heat Exchanger.
   • Cooling water flows in the opposite direction to cool the hot liquid efficiently.
2. The temperature of the sterilized liquid is reduced to the desired level (usually room temperature or a process-specific requirement).
3. Ensure that cooling water flows continuously and is discharged properly.

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Step 7: Output the Sterile Medium

1. The cooled, sterilized liquid exits the system through the "Sterile medium out" pipeline.
2. Collect the sterile medium in a sterile container or direct it to the next stage of the production process.

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Important Points to Monitor

• Steam pressure and flow: Ensure adequate pressure for effective sterilization.
• Temperature at key stages: Monitor preheating, sterilization, and cooling temperatures to meet process specifications.
• Vacuum system performance: Ensure proper removal of excess steam for efficient cooling.
• Flow rates: Regulate input and output flow rates for optimal system performance.