Keep Your Samples Flowing

or

Where can an analyzer get a drink around here?

David Webster P.E.

Solutions, Inc.

Acknowledgements

Bob Ricker – Sentry Equipment

Carl Trantham – Nevada Power

Leonard Zeedyk – Nevada Power

Billie Rea – FPL Energy

The goal is to get each analyzer a drink of The goal is to get each analyzer a drink of water at constant flow and 25water at constant flow and 25°C°C

Sampling 101Sampling 101

• The “Constant Pressure Header” is one keyThe “Constant Pressure Header” is one key

• The “Constant Pressure Header” requires a The “Constant Pressure Header” requires a reliable back pressure regulator/relief valvereliable back pressure regulator/relief valve

The design of a reliable Back Pressure/Relief Valve (BPRV) has large internal orifices, high flow

capacity, and does not plug easily.

This type of Back This type of Back Pressure Regulator Pressure Regulator plugs up easily and plugs up easily and the adjustment knob is the adjustment knob is confusing. It should confusing. It should be set and left alone, be set and left alone, but because it plugs but because it plugs up, the lab techs have up, the lab techs have to stroke it to try to to stroke it to try to clear out the debris. clear out the debris. Also, the diaphragms Also, the diaphragms tend to break easily.tend to break easily.

This panel at a plant This panel at a plant in Colorado has the in Colorado has the BP valve handles BP valve handles removed so no bad removed so no bad adjustments can be adjustments can be mademade

Notice that your new BP/RV’s Notice that your new BP/RV’s cannot be adjusted! cannot be adjusted!

The BPRV acts as a The BPRV acts as a “shock absorber” “shock absorber” and a and a safety valvesafety valve

A good BP/RV has a “flat” performance curve, which means that it will relieve a lot of flow and still keep the back pressure constant.

Do not restrict the BP/RV outlet to the sink!

Sampling 101Sampling 101

• The flow control valve is the second keyThe flow control valve is the second key

Rod-in-tube valve designUse when pressure >500 psi

The two main types of sample flow control valves are selected based on sample pressure

Needle valve Use when pressure <500 psi

The rod-in-tube valve design breaks down Main Steam or Boiler Drum pressure without wire drawing the seat. (Because there is no seat!)

The BP/RV and Flow Control Valve The BP/RV and Flow Control Valve work together to provide a Constant work together to provide a Constant

Pressure HeaderPressure Header

The rod-in-tube valve design relies on small annular clearances between the rod and the tube which can plug up easily with debris & magnetite.

Solutions, Inc SDS-15-SSSolutions, Inc SDS-15-SS

A high capacity strainer will protect the VREL from debris entrained in the sample. Boiler Drum samples are usually the worst offenders

15 in15 in22 strainer surface area strainer surface area

These strainers have approx These strainers have approx 1 in1 in22 of surface area. of surface area.

. The new strainer has 15 times more surface area than the usual sample strainers (Nupro-Swagelok)

Our new strainer design uses an integral blowoff port. When used with a high pressure ball type blowoff valve, this is a reliable way to keep the strainer element clean without requiring disassembly.

Blow the strainer down Blow the strainer down frequently (more during frequently (more during

start-ups.)start-ups.)

How can I tell if my constant How can I tell if my constant pressure header is working?pressure header is working?

The gauges will all read the same The gauges will all read the same (BPRV setpoint), the rotameters will (BPRV setpoint), the rotameters will

stay steady, and there will be stay steady, and there will be ADEQUATE FLOW TO THE SINKADEQUATE FLOW TO THE SINK

The pressure gauges all read the same.The pressure gauges all read the same.

The rotameters stay steadyThe rotameters stay steady

There is adequate flow to the sinkThere is adequate flow to the sink

How do I troubleshoot low sample How do I troubleshoot low sample flow, or if I can’t get 20 psi?flow, or if I can’t get 20 psi?

1. Stroke the VREL to clear debris (40 turns full open to full close).

2. Clean the Nupro Filters

3. Look for excess flow going to an analyzer

4. Check the BPRV diaphragm for a pinhole leak (weeping out the hole).

The Cooling SystemThe Cooling System

• Your new system relies on “lots of flow” through the coolers to control temperature

• If you can hear the tubing rattle, throttle the flow on the top valve a little, just until the rattling stops.

All Sample Coolers are not created equalAll Sample Coolers are not created equal

Many coolers do not have “coil-in-coil” (double helix) and the cooling surface area is not sufficient to give a good “approach temperature”

Double Helix coolers have more surface area and therefore the sample temperature “approaches” the cooling water temperature more closely

• The chiller will maintain 77 ºF within 1 degree.

Some data for Lab folks• Sample velocity of 6’/second is optimum

per EPRI.

Flow rate VelocityTube Size cc/min Ft/sec Lag Time/1000’1/4”x.049” wall 500 2.5 6.5 min

1200 6.0 2.8 min

3/8”x.065”wall 500 0.9 18.7 min1200 2.2 7.6 min1666 3.0 5.6 min

Theoretically correct > 3300 6.0 2.8 minBut not practical

1/2”x.125 wall essentially equal to 3/8”x.065 wall6.0 ft/sec is approximately 1.8 m/sec

Sample Lag TimeSample Lag Time

Erosion/Deposition and EquilibriumErosion/Deposition and Equilibrium

Velocity vs. DepositionVelocity vs. Deposition

Deposition vs. TimeDeposition vs. Time

Handling magnetite & debrisHandling magnetite & debris• Keep velocity up to 6’/sec (1200-1800 cc/min target)

– Keep sample flowing to the sink for “cushion”

• Blow down dirty samples frequently (Boiler Drum)