Keeping gas production clean with WIM Compas, Wobbe index calorimeter and BTU measurement

1.	MATERIAL REQUIRED

The minimum quality grade required for chemicals used in the following procedures is ANALAR.

Cleaning Agents: Demineralised water in a dispensing bottle. Acetone in a dispensing bottle Hardened filter papers Cleaner Solvent (Part No.:- N-180-803) Cleaning Agent, dust remover (Part No.:- N-846-698)

Coating Agent: 50ml ortho-phosphoric acid in 200ml of demineralised water in a dispensing bottle.

Tools: Cell Key. Fine Cleaning Brush (To be kept clean at all times). Digital Multi-meter. Inspection Lamp. Cutters.

2. TEST BENCH PREPARATION

Before handling or coating any cells check the following:-

- Ensure the surface of the Test bench is cleaned down. - Make sure that no work is being carried out that will create any airborne dust/particles. - You have paper towel down on the bench to rest your cells on. In addition place filter  papers down to rest the cell bodies on during coating. - Wash hands thoroughly. - Use disposable gloves. - Use of a bench inspection lamp. Use to check for any cell contamination and that coatings completely cover the cell winding throughout the Cell preparation and testing.

3.	cell check and inspection

3.1	Check that the cell's resistance. Before testing the cell needs to be an open circuit. Using a Taut Band Multimeter set on the x1K? range, place the end the meter probes on the cell electrical contacts and measure the resistance. The following results give an indication of the condition of the cell and in turn whether it will dry down during testing.

Resistance value		Condition

5M? +			Cell in good condition and will dry down. Action: - Test Less than 5M? Slight trace of contamination, should still dry down. - more than 0? Action: - Test

0?				Cell contaminated and will not dry down Action: - Clean until above levels are achieved

If the circuit is closed (0?) either return the Cell to Production Dept/Supplier or Clean as Section 7.0

3.2 	Insert the cell key provided into the hole in the anodised head. Loosen the head; it has a normal right hand thread.

3.3	Unscrew the head carefully without any lateral stress, as the cell former is fragile. When the thread disengages draw the cell former out of the body axially and place the parts on the bench on clean filter papers

3.4	Inspect the Cell, checking the following; - PTFE tube is in place. (Checking it's not come away from the screws clamping it to the body and joined correctly at the top inside the cell tube) - Wires are in place. (Checking it's correctly clamped down by the screws and the rest wrapped tight to the body). - The condition of the glass tube. (Check for cracks or major chips)

3.5	Remove the excess PTFE tube by cutting back to about 5mm from the clamping screw using a small pair of cutters.

4.	COATING

4.1	Wash the windings of the cell body with acetone then allow it to drain for a few seconds.

4.2	Hold the insert horizontally and play a jet of coating agent onto the central portion of the winding, leaving about 5mm at the two ends DRY.

4.3	Rotate the insert so that the central portion is uniformly wetted and so that the hanging drops move towards the end further from the head; most hanging drops will detach when they reach the dry portion of the winding.

4.4	Remove any remaining drops by touching the drops only with the folded edge of a clean filter paper.

4.5   When work with chemicals is completed, return them to the lockable chemical cupboard in their tightly closed original containers and then lock the chemical cupboard.

4.5	Inspect the winding, looking at it against the light. Check that: 4.5.1	the 5mm ends are dry; 4.5.2	the winding is minimally but uniformly coated; 4.5.3	there is a slight fillet of coating along the PTFE spiral; 4.5.4	there are no droplets of coating agent on the spiral.

5.	re-ASSEMBLY

5.1	Slide the insert into the body, allowing only the PTFE spiral to touch the interior of the body.

5.2    Screw the head into the body and tighten firmly using the cell key.

6.	TESTING

6.1	Connect a cylinder of dry gas e.g. 'White Spot' nitrogen, via a regulator set to a pressure less than 4 barg. to the GAS INLET connector of the moisture cell test rig. Use a short length of 1/8 in. OD stainless steel tubing.

IMPORTANT NOTE: - Blow out the Cell rig each time the gas cylinder is turned on, making sure no cells are in the rig. To do this briefly raise the pressure to 6 barg.

6.2	Fit the moisture cell. Look at the gas entries of the cell, one appears to be blind and the other drilled through. The latter is the sample inlet and is marked 'IN'. This should on the same side as the 'IN' marked on the test rig as the cell is slid into the holder.

6.3	Plug the analyser into a mains supply and switch ON so that the cell can start drying down. Turn on the sample supply and set the flow using the needle valve to give an initial reading of 100ml/min on the flow meter connected to the exhaust port on the cell test rig. After 15 mins turn this flow down to 50 mls/min until the end of the test (3-4 hours). Note:- When leaving the to run overnight, reduce the flow down to 20 mls/min. Turning the gas pressure down on the bottle as low as possible to reduce waste.

6.4	Monitor the Cell ppm and Voltage display. Initial readings would be between 1600ppm to 2000ppm along with a voltage of about 4 Volts. The PPM value should fall and the Voltage rise as the cell dries down.

6.5	If the cell PPM does not fall and the Voltage has not reached the 50 volts or more it is likely that the moisture cell is contaminated and will need to be cleaned again. Repeat from procedure 2. As a guide the following voltages give an indication of Cell condition.

Cell Voltage	Interpretation Less than about 2V	Cell probably contaminated or damaged About 2V and rising	Invalid readings, Cell working but wet About 40V and rising	Valid readings, Cell still drying down 50V to 56V	Normal operation More than 56V	Fault condition

6.7	After 1 hour record the reading.

6.8	Every moisture cell should be dried down to less that 10ppm of moisture to do this keep drying them down for approximately 3 - 4 hours recording the PPM result and the time taken.

6.9	One in ten moisture cells should be dried down to below 2ppm of moisture. To do this, dry them down overnight, reducing the flowrate to 20 mls/min during this time as described in section 6.3.

Note:	As the gas cylinder becomes exhausted, the gas becomes wetter. This is because there is moisture absorbed on the internal surface of the cylinder. As the gas pressure becomes smaller this moisture desorbs. The nominally dry gas can become quite wet when the cylinder nears exhaustion. It is suggested that the gas cylinder is renewed before it becomes three-quarters empty.

7.	CLEANING

7.1	Wash the windings with demineralised water and drain.

7.2	Spray the windings with the cleaner solvent, brushing the windings with the fine brush to remove any dirt, especially under the PTFE tubing.

7.3	Spray the cleaning agent (dust remover) over the windings to clean off any excess.

7.4	Wash the windings with demineralised water, then place on filter paper and allow to dry.

7.5	Spray the windings with acetone, and then allow it to drain for a few seconds.

7.6   Check the Cell has an open circuit by following step 3.1.

When it comes to monitoring gas and keeping a safe environment you can find out more on Wobbe index or Combustion air requirement index.