Category: Tech Notes

Your opacity analyzer normally runs fine, but then cold weather sets in and now the opacity readings are a bit flakey, spiky, noisy, weird, unusual, annoying, etc. Well, you should initially rule out the opacity analyzer … it’s not its fault! It’s probably physics! Or earth sciences! But it’s not sunspot activity.

What is most likely happening is:

1. Your stack has significant moisture in its effluent

2. Your purge air system for the opacity monitor draws makeup air from the very cold ambient air

3. When the very cold ambient air meets the very hot, moist stack effluent, the effluent temperature drops significantly

 

…which…

1. forces the relative humidity to approach 100%

2. then forces steam (water) molecules to coalesce (condense) … a phase change

3. then creates visible (water) vapor (some say ‘steam’ but it is really vapor)

4. if you can see it, so can the opacity analyzer’s stack light beam

So, how would you prove this before investing any money in the solution?  How about a very simple test:

1. Somehow stop the purge gas flow temporarily

• block or partially block the blower’s (or blowers’) suction(s)

• turn off the blower(s)

• remove the feeder hose(s) to the injection ports

2. Observe your opacity readings for five to 30 minutes

• did the spiking go away?

3. Re-employ the blower system

• did the problem return?

If answers to questions 2 and 3 are “yes” then you have “Phase Change”

So, how do you fix it? Here are a few ideas:

1. if it only occurs once in a Blue Moon, just declare it on your quarterly reports and take it as “down time”

2. if it happens too often, your Regional EPA won’t enjoy seeing a high down time number

3. install ducting so that the opacity analyzer draws makeup air from a warmed room

4. install purge air preheaters (1500 watts per side minimum; 3000 watts per side for extreme conditions)

Call us at 877-616-0600 to discuss this in greater detail.

There are only two significant things to consider when installing LCW#1 in the OPM2000, OPM2000A, OPM2000R, or OPM2001: [1] over-tightening and [2] stand-offs.

When attaching the LCW to the transceiver’s mounting block, don’t over-torque or over-tighten the four (4) hold down screws. We always recommend “finger tight plus a skosh” (meaning finger tight plus just a tad (smidgen) more). The stack-up is normally in this order: aperture plate – stand-off – o’ring – backing plate (large holed) – LCW – top plate (small hole) – o’ring – screw head. An alternate stack-up can be in this order: aperture plate – stand-off – LCW – top plate (small hole) – o’ring – screw head.

The stand-offs are a factory modification and VERY important to the life span of the LCW. By putting the LCW 3/4″ away from the aperature plate, the beam has a chance to disperse and thus more of the actual LCW active surface area is utilized. This helps prevent “burning” the center out of the LCW (see picture). This is very critical in the OPM2001 as its high intensity beam from the 20 watt halogen lamp will cure the filler material and damage the LC event sites.

Stand-offs promote stability too because more liquid crystal event sites are being utilized if the beam is allowed to spread; as the LCW ages, LC sites tend to lock either open or closed, so if the beam is relying on 1000 events sites instead of 1,000,000 event sites, it will ‘seem” to become unstable sooner as event sites fail due to normal aging.

Parts:

LCW#1: 40F0050R02

 

LCW holding screws: 4-40 socket head, black anodized screws typically

Stand-offs:  4-40, 3/4″, aluminum, hex barrel, male-female

(LC stands for liquid crystal)

Components affected: LCW, liquid crystal window, lamp, barrier window, alignment, bulb, & temperature.

High opacity can come from any of the following:

1. actual stack opacity conditions

2. misalignment

3. failing bulb/lamp or lamp power supply

4. failing LCWs or LCW power supply

5. dust on barrier window and/or corner cube

6. steam that has changed phase to vapor

Call us to help you diagnose this.

Please provide the following:

1. model number

2. age of LCWs

3. age of bulb/lamp

4. reference voltages (8)

5. current ‘run’ voltages (4)

6. temperature

Communication failures typically fall in to 2 categories:

1. bad interconnecting wiring

2. board faults

If you’re not using Belden 8162 or 8163, you run the risk of causing a communications problem that gets worse with time.

The LON originates on the Stack LON board AND the IG-1 serial gateway. If either board is faulted, unpowered, corrupted, blown power supply,  or whatever then you’ll get COMM FAULTS.

Call for more details.

Communication failures typically fall in to 2 categories:

1. bad interconnecting wiring

2. board faults

If you’re not using Belden 8162 or 8163, you run the risk of causing a communications problem that gets worse with time.

The CRU talks RS232 which then routes to a converter (RS232 to RS422) before the signal leaves the CRU. The transceiver receives the RS422 directly without a converter.

Here is the order of typical failures:

1. RS232/RS422 converter in the CRU

2. IO Plexor

3. CPU board in the CRU

Call for more details.

You’re not the first to complain about this! There is a way to “desensitize” both the zero and span pots. It’s usually the span pot that gives you the heartburn; when you just breathe on the pot and your reading changes a 1/2 percent … that’s when you should call us!

The Rosemount 400A hydrocarbon analyzer has the ability to maintain control of its sample pressure at a given value by way of three major components:

1. An internally mounted Siemens-Moore, 0-7 psig, backpressure regulator (BPR)

2. A sample ‘frit’

• Rosemount uses frits for particulate control and to control bypass rates; in essence, it is merely a restrictor that also has filtration capability

• According to the Mott Corporation, “These frits protect HPLC (high pressure/performance liquid chromatography) columns from particulate contamination and distribute dissolved samples evenly for optimal column performance.”

3. An unrestricted bypass vent line

To be perfectly stable and precise, everything has to be a constant. That is, the BPR has to maintain its characteristics, the frit has to exhibit the same pressure/flow characteristics, the exhaust must remain open and ‘appear’ as near atmospheric pressure, and the sample pressure must remain constant. Let’s look at these in a little more detail.

The BPR:

1. Maintaining a constant pressure at the head of the capillary is critcal to ensure a consitant sample flow rate to the burn and is the primary function of the BPR.

2. As upstream sample pressure increases, the BPR valve will open and allow more flow to the bypass vent while maintaining the setpoint pressure.

3. As upstream sample pressure decrease, the BPR valve will close, causing less flow to the bypass vent whie maintaining the setpoint pressure.

4. Therefore, the bypass rate for a normally operating system should be set high enough to accomidate a reduction of sample supply pressure, but low enough to allow for increases in pressure without flooding the bypass vent.  Rosemount recommends .3 to 3L/min of bypass which should be set by controlling the sample pressure to the analyzer after the the desired BPR setpoint is acchived.

The Frit:

1. A normal frit will allow the Rosemount 400A to create 1500 cc/min of bypass with the BPR set to 5 psig and the sample delivery pressure set to about 8 psig.

2. A fouled frit will require a higher sample source pressure in order to maintain the same bypass rate. You could also lower the BPR setpoint but in our application the internal sample pressure must be held at a constant value in order for the sample capillary to deliver the correct sample flow to the burner.

3. Removal of the sample frit will cause internal pressure control to be almost impossible and will result in either low unstable pressure control when sample source pressure is below the 5 psig of the BPR, or unpredictable pressures when sample source pressure is above the 5 psig setpoint of the BPR.  When  the flow limitations of the BPR are exceeded the BPR will  start “singing” as it attempts to shunt the excess pressure by dumping significant volumes of sample to the bypass vent line.

The Bypass:

• The bypass vent line should be unrestricted, however, it is not as critical to pressure control as the first two items.

Restrictions in the vent line will result in increased pressure at the capillary head which will increase the display reading.

Use the link below to download our Beckman/Rosemount 400 or 400A lighting procedure.

Here are some typical reasons for lighting failure:

1. Not enough fuel getting to burner (clogged fuel restrictor at burner base)

2. Glow plug is bad (or glow plug transformer has failed)

3. Thermistor is bad (or not plugged in)

4. Not enough air (oxygen) to support combustion (clogged air restrictor at burner base)

5. Air leak in chimney (typically the assembly separates from the burner base during shipping causing a leak & dilution of the fuel)

RIGAS-FID_400A_lighting_instruction_r1.pdf