D-R 290 Dust Concentration and Opacity Monitor

■ In-situ measuring principle, continuous measuring

■ Long life solid state light source

■ Optimal evaluation of measuring signals due to a Super Wide Band Diode (SWBD).

   Measurement is more stable than with conventional LED systems.

■ High performance microprocessor technology

■ LC Display in opacity, optical density or in mg/㎥

■ Automatic zero and span check with soiling correction of measured values

■ Optics and electronics in a hermetically sealed housing

■ Simple alignment without special tools

■ Reduced maintenance due to advanced purge air system

■ Programming via control display unit or remote bus interface

■ Measuring data available as analog current or via bus interface

■ Two analog output signals available with switchable ranges

■ Transmission – Dust

The photoelectric measurement of the transmission T (=irradiation capability) is based on the determination of the attenuation of light sent through a gas containing dust particles.

 Several systems are implementing a narrow-band LED light source with a spectral response between 500 and 600 nm using the light which is directly emitted from the LED. Therefore the response is temperature dependent.

The DURAG Super Wide Band Diode SWBD, with a spectral response substantially

enlarged to 400 – 700 nm, results in a more stable measuring system with results that

are more constant. A blue Gallium Nitrite diode in connection with a fluorescent layer produces a white light, which contains the broad band of wavelengths associated with the luminescence material as well as the emission band of a normal light emitting diode.

From the Transmission, the dust load can be displayed either as Opacity O or Extinction (optical density)E.

The Opacity can be compared with the attenuation of light and shows the percentage of absorbed light. The Opacity measurement is used mostly in the USA and Asia. The advantage of Opacity is that the measuring devices must not be calibrated. The disadvantage is the dependency of the measuring result from the measuring location.

Although there is a re-calculation from the monitor location to the stack emission outlet, the influences from the color, the shape and the surface structure of the particles are not taken into account. Due to the non-linear relationship between the dust load and the opacity, the opacity is increased by only approx. 15% when doubling the dust load in the upper measuring range.

The Extinction (optical density) runs linear to the dust load due to taking the logarithm: Doubling the dust amount results in the display of the unit doubling. Extinction is used in European countries and increasingly also in Asia. By calibrating the measuring location (not the measuring device) according to VDI 2066 or EPA CFR 40 Part 60 # 5, an exact display of the dust load in mg/㎥ is achieved. The site depending extinction coefficient k is defined by gravimetric comparative measurements. According to the smallest quadratic error from at least 15 single measurements, the calibration curve is calculated for the measuring location. Under normal operating conditions we have to assume that the same dust load con lead to different readings depending on grain size and flow distribution. There fore it is not have a calibration curve, but also uncertainty ranges Y1, Y2 and Y3,Y4 have to be considered.

■ Application

The DURAG D-R 290 Opacity and Dust Concentration Monitor is used for continuous opacity or dust monitoring  of flue gas in stacks and ductwork. According to TA Luft and 13. and 273 BlmSchV the D-R 290 is suitable for

■ systems firing coal, fuel oil or a mixture of fuels

■ Converter plants, asphalt mixing plants and cement production plants

■ any other type of plant requiring quantitative monitoring of opacity or dust concentrations. Measured results can be displayed as opacity, optical density or in mg/㎥.

■ Principle of Operation

The D-R 290 operates according to the principle of auto collimation (double-pass).

The light beam crosses the measuring part twice. The system measures and evaluates the attenuation of the light beam caused by the dust in the measuring path.

 A photo element alternately receives the measurement and comparison light beam. Switching between the measurement beam and a comparison light beam proceeds through an electromagnetically actuated rotary diaphragm. For check value compensation, comparative measurements of 2 seconds in duration occur every 2 minutes. There is only 1 joint amplifier for the measuring and the comparator beams, thus compensating temperature influences as well as for amplifier long-term drift. The transmitted light is generated by a SWBD (Super Wide Band Diode) without the influence of other light source, such as sunlight. An SWBD also has a long life span compared to traditional halogen lamps. Because of the broad nature of the SWBD, the measurement results are not influenced by temperature or other factors. The use of the wide band diode also offers a more stable measurement than a conventional narrow band LED.

The D-R 290 is equipped with two analog measurement value outputs. Each of the outputs has two selectable extinction or opacity ranges. The measurement ranges are selectable from 0..0.1 to 0.. 1.6 for extinction, and from 0..20 to 0..100% for opacity. Opacity computation of the opacity at the stack outlet by means of the stack correction factor possible. For proper functioning the D-R 290 periodically performs a check cycle, measuring and indication the zero point, the soiling of the optical boundary surfaces as well as a reference value automatically. If necessary, the subsequent measuring values will be corrected. If the correction surpasses a freely programmable value, a corresponding indication will be generated. Condensation and deposits are avoided by using a heated pane.

■ Scope of Delivery

■ Mounting flan gas

■ Measuring head

■ Reflector

■ Display and operating panel, 2 m connectivity cable

■ 1 purge air fan

■ Optional Accessories

■ Bus interfaces, Modbus

■ Automatic fail safe shutters as a protection for the measuring head and reflector in case of an outage of the purge air

■ Weather protection hoods when the instrument is mounted in an unprotected area

■ Explosion proof execution with EEx-p protection methods possible

■ Additional on-stack display panel, thus remote display and operating panel connectable up to 500 m.

■ Temperature compensation through additional analog input.