WOBBE INDEX ANALYZER (CALORIMETER)

FlameThe BAGGI BA-WIA is an on-line process analyzer for combustible gases. It measures the following quantities in real time

· Wobbe index

· Calorific value

· Specific gravity

Typical combustible gases are:

· Natural gases

· Blast furnace gases

· Coke oven gases

· Liquefied petroleum gases air mixtures

· Biogas

 

The instrument is a high speed combustion calorimeter, controlled by an embedded computer with a VGA display. A small flow of process gas is burnt continuously and the related temperature rise is measured by a thermopile. The electrical voltage at the output of the thermopile is a function of the Wobbe Index value. The Specific Gravity value is measured by a dedicated sensor. Then the computer calculates the Calorific value by the formula:

 

_____________

Calorific value = Wobbe index · ÖSpecific gravity

 

 

The BA-WIA is made up by adding to the calorimeter a complete sampling system. Please refer to the picture.Calorimeter

A typical system for dirty gases such as blast-furnace gas and coke oven gas is described hereafter.

An electrical heating cable and the related thermostat are provided to regulate the temperature of the fast loop pipe between the process and the calorimeter (required when naphtha is present). Then the sample gas undergoes a three-step filtering process:

1- Absolute filter (dust removal)

2- Bubbler (naphtha removal)

3- Coalescent filter (humidity removal)

The absolute filter needs a frequent cleaning; therefore it is redundant to avoid affecting the analyzer operation during the clean-up. A set of valves allows to disconnect from the process the filter to be cleaned and to connect it to a blast of Nitrogen for cleaning the cartridge. Two options are available:

· the valves are controlled electrically (solenoid valves) by a PLC that performs periodically an automatic switchover and cleaning;

· a pressure sensor, across the filter, raises an indication when the differential pressure is too high and the human operator needs to manually actuate the valves for switchover and cleaning.

Finally the sampling system is completed by an optional suction pump.

The standard analyzer has one process gas inlet and one calibration gas inlet; both inlet ports come with pressure regulators.

When the composition of the process gas can change widely, the dual range option is available: the calorimeter is delivered with two internal Wobbe jet orifices, with appropriate diameters. In this case, a second calibration gas inlet is present. The embedded computer is able to switch automatically to the correct flame orifice according to the Wobbe index of the input gas mixture.

BAGGI ships the certified calibration gas cylinders.

An additional option allows measuring the W.I. of gases with very low burning capability. A carrier gas (such as Methane) is added to the process gas to support combustion. The embedded computer takes care of the correct parameters for calculating the Wobbe Index.

ATEX proof shelters are available for systems having to be operated in potentially explosive atmospheres.

Specifications

Measurement range according to the calorimeter configuration:

the lower end is between 700 and 1400 kcal/Nm3 (less than 700 kcal/Nm3 with carrier gas)

the higher end is between 15000 and 30000 kcal/Nm3

Accuracy: ± 1% full scale

Response time: 20 sec (T90)

Ambient temperature: between 5 °C and 35 °C

Power supply: 220 Volt / 110 Volt, 50 / 60 Hz AC, 200 W

Dimensions: height 1020mm x width 720mm x depth 337mm (calorimeter only)

Input/Output interfaces:

· Graphical User Interface

· Analog outputs (4 ÷ 20 mA) for Calorific value, Wobbe index and Density

· Digital outputs (Normal Operation, Maintenance, Air Filter Change, Fault, WI Out of Range, Absolute Filter ΔP)

· Digital inputs (Start Measurement, Start Calibration, Hold Output signal, Solenoid Valves Control signals)

· Serial line (optional RS232/PROFIBUS)

 


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