Codel - Model VCEM5000 - Gas Velocity Monitor
The VCEM 5000/51000 represents the latest generation of CODEL’s unique flow monitors. These systems measure the velocity of stack gases using a highly accurate time of flight measurement that is derived from a cross correlation analysis of the infra-red emissions of the turbulent gas. Two robust infrared detectors are used for the prime sensing, mounted on the stack or duct typically 1m apart in the direction of flow. High efficiency air curtains are fitted to considerably extend the time between maintenance periods and window cleaning (typically 1 year).
- Non-contact infra-red sensing
- Continuous measurement
- Suitable for hot and dirty gases
- No limit on upper gas temperature
- No moving components
- High availability, low maintenance requirement
- Large Combustion Plants
- Small Combustion Plants
- FGD (Flue Gas Desulphurisation)
The VCEM 5000/51000 represents the latest generation of CODEL’s unique flow monitors. These systems measure the velocity of stack gases using a highly accurate time of flight measurement that is derived from a cross correlation analysis of the infra-red emissions of the turbulent gas.
Two robust infrared detectors are used for the prime sensing, mounted on the stack or duct typically 1m apart in the direction of flow. High efficiency air curtains are fitted to considerably extend the time between maintenance periods and window cleaning (typically 1 year).
This technology offers significant benefits over other types of flow measurement devices.
- Non contact technology enables operation on hot, dusty and aggressive gases
- It measures directly the bulk gas velocity
- No moving components delivering low maintenance, and high measurement availability
- Can operate at gas temperatures in excess of 1000 deg C
- Equipped with full high and low span automated span checks
The VCEM 5100 is a standalone unit which can be easily integrated into an existing or proposed CEMS system. It includes a dedicated Data Dislpay Unit for local data interrogation.
The VCEM 5000 is a unit dedicated for use in a CODEL SmartCEM System where all the analysers communicate via a Station Control Unit (SCU). This exports data to the CODEL SmartCEM data logging system, which displays real time data and logs data for historical analysis and regulatory reporting.
Computation of Total Pollutant Release
Legislation often demands that emission measurements are presented in mg/Nm3 where the expressed volume has been normalised to a standard temperature, pressure and oxygen concentration, and where the effects of dilution by water vapour have been removed.
To compute a measurement of the total pollutant release to atmosphere in kg/hr (or tonnes/annum), it is necessary to know:
- The pollutant concentration in mg/m3 (mg per actual m3)
- The hot gas flow in m/s
- The cross sectional area at the point of measurement in m2
The total release is then calculated as follows:
Mass flow = Mass concentration x Gas velocity x Area of Duct
It is vital that all measurements are made on the same basis. Attempting to make this calculation using an actual hot wet gas flow in m/s and a normalized gas concentration in mg/Nm3 will produce significant errors.
The method used is similar in principle to the technique of flow measurement by the injection of chemical dye or radioactive tracers, where the velocity is derived from the transport time of the tracer between two measuring points a known distance apart. Instead of an artificial tracer being added, the naturally occurring turbulence of the gas stream is used as the tracer.
This flow turbulence causes fluctuations to occur in infrared radiation emitted by the gas. This continuously variable turbulent pattern is monitored by two infra red sensors mounted typically 1m apart along the direction of gas flow. An electronic correlation technique is used to continuously compare the two sensor signals to determine the time delay between them imposed by the gas velocity.
Typical signals from the sensors A and B are shown here. The signal from sensor B shows a strong similarity to that from sensorA but is delayed by a time t, the time taken for the gas to flow from point A to point B
Continuous determination of the sensor signal time delay by the signal processor unit produces a continuous measurement of gas velocity since:
- Velocity V = L/t
L is the separation distance between the two sensors.
- Operating Principle: Infrared correlation
- Measuring units: m/s, m3/s
- Ambient Temperature: -20°C to +50°C
- Power supply: 48V DC from Signal Processor Unit (SPU)
- Construction: epoxy-coated aluminium to IP67
- Analogue outputs: 2 x 4-20mA current outputs as standard, isolated, 500Ω load max, fully configurable
- from keypad
- Logic Outputs: 2 x volt-free SPCO contacts, 50V, 1A max, configurable as alarm contacts
- 1 x volt-free SPCO contact, 50V, 1A max, for data valid signal
- Serial Data: RS232/RS485 MODBUS protocol (Optional)