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BLENDAIRE II PACKAGED LPG MIXING SYSTEM

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The State of the Art Mixing System

BLENDAIRE II LPG MIXERS

The Blendaire II is a state-of-the-art packaged LPG mixing system that uses a proprietary control system housed in a SIEMENS PLC for mixing gases in parallel streams. It is a versatile gas mixing system for LPG and air mixing, manufactured gas, or natural gas conditioning — and replaces conventional piston mixing systems with significant performance and cost advantages.

 

The Blendaire II is the ideal solution when very accurate calorific value (CV) control is required for an industrial process, or when there are changes in the quality of the feedstock. It delivers a premium grade mixing solution for the most stringent gas quality requirements.

.​​The Blendaire II Solution — Feed Forward Control

The Blendaire II uses a feed-forward control system that prevents mixing errors from occurring before they can happen. Here is the step-by-step process:

 

1.  LPG vapour at regulated pressure passes through a flow meter and enters the mixing section of the Blendaire II.

2.  The LPG flow signal is sent instantly to the SIEMENS PLC.

3.  The PLC converts the signal into a standard flow rate using real-time pressure and temperature data from transmitters located near the flow meter.

4.  The PLC calculates the exact air flow rate needed to achieve the correct mixing ratio — based on line pressure, temperature, and the assumed CV value of the LPG.

5.  The PLC issues an immediate command to the air flow control valve — before the two gases mix. The signals occur instantaneously.

6.  The valve positions itself precisely according to the flow coefficient — the defined relationship between valve position and flow rate based on current differential pressure across the valve.

7.  The actual air flow rate measured by the flow meter is compared with the required flow rate and fine adjustments are made automatically.

8.  Compressed air mixes with the LPG. The resulting SNG pressure equals the LPG inlet pressure — no additional pressure management required.

Blendaire II for SNG mixing systems

The Feedback Loop — A Final Safety Check

In addition to the feed-forward system, the Blendaire II also includes a feedback loop as standard. This performs a final quality check to ensure the gas mixture is exactly as required. Any discrepancy detected is fed back to the feed-forward control loop for overall compensation of all errors — including those associated with measuring instruments and the assumed CV value of LPG. This dual-layer system delivers the highest level of accuracy and protection available.

Start-Up Performance

The Blendaire II responds immediately upon activation. The valve accounts for momentary unbalanced downstream pressure from the very first moment — setting itself to the approximate correct position instantly, without waiting for any feedback signal. Fine adjustments follow rapidly and accurately. This fast start-up response also enables full automation of the load tracking process.

full installment of Blendaire

Safety Features


Due to the extreme simplicity of the system, chance of mechanical failure is virtually nil. There are only three moving components in the BLENDAIRE II – two flow meters and one air flow control valve. It is designed to be fail-safe with TEN elements of protection incorporated. The mixed gas outlet valve will be shut off immediately upon any of the following circumstances:​

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  • If the LPG flow meter fails to move or send out signals

 

  • If the air flow meter fails to move or send out signals

 

  • If there is a substantial discrepancy between the actual and required air flowrate, as it may indicate the malfunction of the air flow meter or control valve

 

  • If there is a substantial discrepancy between the air pressure downstream of the control valve and the mixed gas as it may also indicate the malfunction of the control valve

  • If the air flow control valve fails to receive a signal or move according to the signal(s) received

 

  • If any of the pressure and temperature transmitters for LPG and air fails to transmit signals to the PLC

 

  • Low LPG temperature, and high/low LPG/air pressure, etc. are normally safeguarded up stream of the blender, but even if it happens it will not affect the safe operation of the BLENDAIRE II system at all as long as there is no condensation of LPG within the system. If desired limits may be set to shut off the mixed gas outlet valve as well.

  • If the gas quality deviates from the setpoint exceeding a preset limit for ANY REASON

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  • Any channel in the input and output module of the PLC fails

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  • The CPU of the PLC fails After the mixed gas outlet valve is shut, an alarm with an easy-to-understand message in English or an alternate language is issued for quick identification of the problem. The outlet valve can be reopened after the problem has been rectified. Optionally a software warn standby or hardware hot standby system for the CPU can be added. In case the active CPU fails all its duties will be automatically transferred to the standby one. The transfer is transparent to the user as there will be no interruption of the process or loss of any data.

Blendaire II for natural gas mixing systems

Advantages of the BLENDAIRE II System


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  • Fail-safe design with many safety features included

  • Informative alarm messages (with optional logging function) for quick identification of faults

  • Simplicity in construction minimizing the chance of mechanical failure

  • High confidence of reliability as all major components used are standard and matured products made by reputable manufacturers, hence

  • Proven reliability

  • In general, very short delivery lead-time

  • Replacement components and parts are readily available on the market at reasonable price

  • Fast response and very accurate blending with both feed forward and feedback control

  • Very wide range of mixing ratio easily adjustable without modification to the hardware configuration

  • Smooth start-up and operation for maintaining consistent gas quality at all times

  • Turndown ratio is the same as the LPG and/or air flow meters, which is typically 40 to 1 or better

  • Automatic load tracking at low loads (optional) making turndown ratio no longer a concern. The mixed gas outlet valve will be set to shut off above a certain pressure or below a certain flow rate, and re-start at a lower pressure, all automatically

  • Only clean air will pass through the control valve, hence there will be no blockage of orifice or sticking of moving mechanism by impurities in LPG, or the need to clean them at regular intervals

  • Low LPG pressure required – the same as required for mixed gas, making it possible to vaporize LPG at lower temperatures to avoid formation of polymers from unsaturated hydrocarbons. There will be less need to run the LPG stabilizing pump, meaning less wear and tear and less energy consumption

  • Low compressed air pressure required, meaning less energy consumption and longer motor life

  • Changing the mixed gas pressure is as simple as changing the outlet pressure of the LPG regulator

  • Dual streams can be mounted in a single skid with only one LPG and air inlet and one mixed gas outlet for simpler installation

  • One integrated control panel for multiple stream blenders

  • Industrial standard Profibus DP communications capability for easy integration with the central control system; other communication options are also available

  • High capacity per stream means lower equipment and installation cost

  • Total corrected and uncorrected flow information available from the two meters without the need of an additional total flow meter – a substantial saving in the total system cost

Product Information

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Product Brochure

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ExVeritas ATEX Certificate

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FM Certificate of Compliance

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PED Certificate

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