MONITOR REGULATOR SIZING AND OTHER CONSIDERATIONS

Transcription

1 MONITOR REGULATOR SIZING AND OTHER CONSIDERATIONS 6" 4" 6" 4" 4" 8" 4" 6" 6" 8" 6" 6" OGA 015 Regulator Fundamentals Seminar

2 Monitor Regulator Sizing Theory FLOW in m out USTREAM MONITOR REGULATOR DOWNSTREAM REGULATOR CONTROL REGULATOR Maximum flow occurs through the regulator when: 1. The flow through the upstream regulator equals the flow through the downstream regulator. At the given pressure conditions and 3. Both regulators are wide open

3 Definitions 1) Flow Coefficients: C v... Water (GM) through valve@ 1 SI DRO. C g... Air specific gravity of 1.0 C 1... Efficiency coefficient (range 15 40) C g /C v X T... The pressure drop required to produce critical or maximum ( Valves flow through the valve (Fisher Control... Natural gas coefficient ( 0.6 specific gravity) ( cp/cv ) k... Ratio of specific heats : NOTE Flow coefficients are stated in SCFH by the manufacturers 3

4 Definitions ) ressures: inlet ( SIA )... ressure m ( SIA )... Intermediate ressure outlet ( ressure(sia... Outlet 3) Flow Types: a) Non-Critical (sub sonic) Flow Gas velocity not yet at the speed of sound b) Critical (sonic) Flow Gas velocity at the speed of sound c) Speed of sound in natural gas 1377 ft/sec for.6 Sg gas at standard temperature & pressure 4

5 Flow Equations ( Sonic 1) Non-Critical flow (Sub ( a Q Outlet Outlet Universal Gas Sizing Equation ( b Q 1 S g C g 3417 sin C1 Outlet deg 5

6 Flow Equations ( Sonic ) ) Critical flow ( a Q Universal Gas Sizing Equation ( b Q 1 S g C g Q 1.91 C g 6

7 The Rule of Forbidden Signals: producedchangespressureofeffectthe by a body moving at a speed faster than the speed of sound cannot reach points aheadofthebody. (von ármán, Jour. Aero. Sci., Vol. 14, No. 7 (1947)) This rule can be applied to pneumatic flow restrictors where the body is not moving, but flow velocity relative to the body can reach, or exceed, the speed of sound. Whenever the downstream pressure is low enough to produce Mach 1 at the restrictor throat, any effect of changes in the downstream pressure cannot reach points upstream of the throat. Thus, flow rate will be independent of downstream pressure. This situation applies to a single orifice restrictor flowing gas when the overall pressure ratio exceeds

8 Determination of Non-Critical / Critical Flow The critical pressure conditions depend on the ratio of the specific heats Factor as stated below The value of the specific heats ratio Factor k is equal to k 1.7 for natural gas k In k1 out k

9 Non-Critical / Critical Regulator Equations 1) Non-Critical (sub sonic) Flow Outlet Q Outlet Outlet Q 1 S g C g 3417 sin C1 Outlet deg ) Critical (sonic) Flow Outlet Q Q 1.91 C g 9

10 Manufacturers Capacity Tables An alternate method is the manufacturers capacity tables. Tables provide capacity at various pressures Recommended pressure & spring limitations Also these tables should be reviewed when sizing by equations for: ressure limitations Spring limitations and Available orifice sizes 10

11 Determination of Intermediate ressure m? Upstream Regulator Downstream Regulator 11

12 Determination of Intermediate ressure m 1) Non-critical flow where regulator flow coefficients m c m Outlet Outlet Outlet ) Critical flow where regulator flow coefficients m c 4 m or m

13 Capacity Calculation rocess FLOW STE BY STE ROCESS DETERMINE: in m out USTREAM MONITOR REGULATOR DOWNSTREAM CONTROL REGULATOR 1) SONIC / NON-SONIC ACROSS REGULATOR SETTING. (/Outlet) ) INTERMEDIATE RESSURE m. 3) SONIC / NON-SONIC ACROSS USTREAM REGULATOR. (/Intermediate) 4) FLOW RATE ACROSS USTREAM REGULATOR. (/Intermediate) 5) SONIC / NON-SONIC ACROSS DOWNSTREAM REGULATOR. (Intermediate/Outlet) 6) FLOW RATE ACROSS DOWNSTREAM REGULATOR. (Intermediate/Outlet) 13

14 Sample Calculation in 50 sig out 5 sig Add 15 sia to the inlet and outlet pressure to make them absolute pressures Question: Is in/out greater or less than 1.814? Outlet in out? Less than FLOW in m out USTREAM MONITOR DOWNSTREAM CONTROL REGULATOR REGULATOR Determine the intermediate pressure m m Outlet m SIA Outlet Outlet 14

15 Sample Calculation Determine the capacity of the upstream regulator Do we have Sonic flow? in m 54.4 Q Q 1 in m m Q 4.0 Mscfh Determine the capacity of the downstream regulator Do we have Sonic flow? m out 40 Q Q 1 m out out Q 4.0 Mscfh 15

16 Sample Calculation If you have a design flow rate of 100 MSCFH: What size flow coefficient do you need? Good regulation is between 80% to 90% of maximum calculated capacity of regulation. Therefore, divide the required flow rate by 0.8 and divide by the calculated flow rate. Example: 100 MSCFH MSCFH 5. 16

17 3) Non-Critical flow where Regulator flow coefficients m c 4) Critical flow where Regulator flow coefficients m c c m Outlet Outlet c m Outlet c m m m 4 1+ c m 4 m C Determination of Intermediate ressure m 17

18 Determination of Intermediate ressure m in 100 sig out 35 sig, (m ) (c 1) Add 15 sia to the inlet and outlet pressure to make them absolute pressures Question: Is in/out greater or less than 1.814? in 115 sia m? sia out 50 sia m c 1 Outlet? in out Determine the intermediate pressure Critical flow where Regulator flow coefficients m c m 4 1+ m c 4 m C 18

19 Intermediate ressure m Sample Calculation Determine the intermediate pressure Critical flow where Regulator flow coefficients m c m m 4 c 1+ 4 m C in 115 sia m? sia m c 1 out 50 sia m sia 19

20 Intermediate ressure m Sample Calculation Determine the capacity of the upstream regulator m in m ( m ) ( c 1) Q Q in m m Q 54. Mscfh Determine the capacity of the downstream regulator c 1 in m Q m 108. Q 1 Q 54.1 Mscfh 0

21 Conversion Equation for C g & C 1 Values to Values Note: Cg values are in SCFH log 3417 C 1 C g 1.91 Conversion Equation for C v & X T Values to C g Values C g 40 C v X T C 1 C C g v 1

22 Sizing of Regulator Risers Use gas velocity for sizing the diameter of the inlet & outlet risers on regulator settings D in Inches, Q in Mcfh, 40 MH in sia D 3.61 Q 58.7ft sec 60 MH D.95 Q 88ft sec Q 80ft 54.5 MH D 3.00 sec 80 feet per second is defined by AI 1 as the erosion velocity V el Q sia + flow flow Mcfh sig D MH V el MCF Hr 1000ft MCF sia sia + flow sig 1Mile ft π D inch 144 inch ft

23 Regulator Flow Curves Capacity Curves for Monitor Regulators 5 to 70 SIG Outlet ressures 3

24 Regulator Flow Curves Instructions for calculating maximum capacity of a monitor set of regulators with identical orifice. 1. Locate inlet pressure curve on chart from previous slide. Locate maximum outlet pressure along Y axis 3. From the outlet pressure, follow the line across the chart left to right, until it intersects the inlet pressure curve 4. Draw a vertical line down and read the base capacity along the X axis 5. To obtain the capacity of a set of regulators, with a value greater than or less than the base capacity value of 1, multiply the base capacity by the value of the regulators 6. EXAMLE: Calculate the maximum capacity of a monitored set of Sensus S regulators equipped with a 1 innerseateddouble ½ valves. value equals 4.7. The inlet pressure is 60 psig and the outlet pressure is 35 psig 4

25 Monitor Regulator Sizing Charts 1. Monitor Regulator Flow Curves a. Simple ease to determine monitor set capacities b. No calculations required. Monitor Regulator Flow Chart a. Ease to follow step by step b. Can be used for programming 5

26 Monitor Regulator Capacity Calculation Flow Diagram in m out Upstream Downstream k m 4 k c in m k m 1 4 k c Yes NO in out No YES m k m k c in out k m k c in k m k c out 4 out m in m YES in Q k m out YES m Q k NO NO m out Q k in m Q k m out Q m MSCFH Q c MSCFH Q m Q c 6

27 Regulator Outlet Droop 1. What is Droop? Droop is the decrease in outlet pressure from the set point. As flow increases from the set point to maximum capacity. Spring and Diaphragm effect. As the spring gets weaker (expanding) the diaphragm area gets larger. Therefore, a lower pressure under the diaphragm will balance the force of the spring at a greater valve opening Lock-up pressure 100% 99% Set point boost Droop 98% FLOW RATE > 7

28 Regulator erformance Curves 8

29 Regulator erformance Curves NEW LOC-U RESSURE X NEW SET OINT 15 9

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