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Join Date: Nov 2008
Posts: 4

Use of Y type control valve

11/28/2008 8:30 AM

Dear All,

As a new comer I found u r doing a great job here

My question is I have seen a Y type control valve with pneumatic actuator in the LNG line of BOG Compressor

I wonder there must be a specific reason for this.

Can anybody explain please?

Thanks a lot

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Power-User
United States - Member - US Citizen - Born & Raised Engineering Fields - Control Engineering - HVAC/R Simplified Using PLC Controls Engineering Fields - Instrumentation Engineering - HVAC/R Simplified Using PLC Controls Engineering Fields - Energy Engineering - HVAC/R Simplified Using PLC Controls

Join Date: Mar 2007
Location: Brick, NJ (USA)
Posts: 110
Good Answers: 5
#1

Re: Use of Y type control valve

11/28/2008 10:05 AM

Here is a PDF link of 52 pages detailing, with illustrations, the design and functionality of the Hamworthy Corporation Natural Gas Liquification and Regasification systems on a transportation carrier. Details of their Boil Off Gas systems are included.

I hope this helps you understand the various valves, compressor systems, coolers, etc.

http://www.thedigitalship.com/powerpoints/SMM06/lng/Reidar%20Strande,%20Hamworthy.pdf

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Participant

Join Date: Nov 2008
Posts: 4
#3
In reply to #1

Re: Use of Y type control valve

11/28/2008 11:01 AM

Dear Sir,

Thanks for ur help but that link not covers control valves

My question is apart from space saving what r the uses of Y type control valves

Thanks

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Anonymous Poster
#4
In reply to #3

Re: Use of Y type control valve

11/28/2008 12:03 PM

If you are simply asking about the function/advantage of a Y-type valve - it is this:

You generally get lower pressure-drop / better flow characteristics through a Y-pattern because it is more "inline" with the flow of fluid. In a regular 90 deg. globe (or other) the flow has to make 2 - 90 deg turns through the valve.

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#2

Re: Use of Y type control valve

11/28/2008 10:41 AM

Thought this might help explain the pneumatic valve, also.

A description by Ricardo Simeoni, Industry Monitor NC O&G CCI, Rancho Santa Margarita, CA

World's largest LNG complex. (Control Valve Technology)

When the latest two-train LNG plant in East Malaysia comes on line in 2003, this production complex, Plants 1, 2, and 3, will be the world's largest such facility - producing 23,000,000 mt/yr (70,000 t/day). This new two-train liquefaction facility with an annual LNG production capacity of up to 3,400,000 mt/yr (10,250 t/day) in each train is to be built along with an LNG storage tank having a capacity of 120,000 m3 (4,250,000 cu-ft). Incorporating the latest available LNG technologies, it features air cooling throughout and a high efficiency system design that maximizes the utilization of the turbines' power together with its physical protection for total reliability.

Among the advanced technologies employed are 30 severe-service anti-surge compressor recycle valves designed for low noise (85 dBA with bare piping) output and quick operation (less than 1 sec. fully open to fully closed), 34 depressurizing valves for emergency and maintenance shutdown purposes, and 34 miscellaneous, severe-service control valves , mostly for flare control purposes, Figure 1.

Anti-Surge Recycle Systems

Essentially, an anti-surge, recycle system functions by maintaining the minimum flow required to avoid surge conditions for the established compressor speed. Regardless of design or application, centrifugal compressors have one common characteristic i.e., at low flow, due to high external circuit resistance, orderly gas flow through the compressor is impossible because gas velocities are too low to be converted to the required pressure energy level in the discharge line.

When compressor discharge pressure exceeds impeller discharge pressure, gas backflow occurs until the compressor discharge pressure become less than impeller discharge pressure. At this point, forward gas flow is re-established, and compressor operation is nearing unstable conditions, resulting in vibration and possible damage to the compressor itself. This phenomenon or stall produces a surge in the system. As a function of its design, every centrifugal compressor has a stall/surge point at any given operating speed. While the gas flow corresponding to this surge point is fixed for a constant-speed compressor, it changes at each operating speed for a variable-speed compressor.

In any event, good industry practice dictates that compressor gas flow should never drop below 5 percent in excess of the surge point for any operating speed. It is for this purpose that compressor recycle valves are used to recycle gas flow from the compressor discharge to suction as needed to prevent operation below this critical flow.

Recycle Valves

Recycle valves perform two basic functions: react quickly during startup, shut-down and, emergency situations; and modulate recycle flow during normal system operation to avoid compressor operation near or below the critical surge point.

Figure 2 shows typical recycle valve control integration into the compressor cycle. Figure 2a indicates the relationship of the four critical flow points for three typical compressor operating speeds. Figure 2b indicates safety on response, an operating feature of the control system.

[FIGURE 2 OMITTED]

If any line is crossed, the control and recycle trip lines will be moved to the right by X percent because their position is assumed to be too close to the surge point. If, crossed three times, the compressor will trip.

The main problems generally associated with compressor recycle valves include: High noise potential; vibration; inadequate response time to fully open a closed recycle valve on system upset; control instability (hunting) due to improper actuator and/or controls selection; and inadequate capacity for all service condition

High noise levels in excess of 100 dBA with bare piping can be experienced with conventional recycle valves. Severe vibration is thus created because the high mass flow at high pressure drops. This can cause valve and trim fatigue failure and also lead to pipe failure.

Recycle Valve Ratings And Design

The 30 anti-surge recycle valves range in size from 4 x 4 in. (100 x 100 mm) up to 24 x 32 in. (600 x 900 mm). Capacities are as high as 236 kg/sec (31,000 lb/hr) with inlet pressures up to 70 BarA (1000 psig) and [DELTA]Ps as high as 59BarA (860 psi) at temperatures up to 96 [degrees] C (205 [degrees] F).

In order to meet the less-then 85 dBA with base piping specification, these anti-surge compressor recycle valves, Figure 3, incorporate a tortuous flow path through multiple, right-angle turns within a stack of individual disks, Figure 4. These disk stacks completely surround the plug throughout its stroke. In this manner, velocity heads: ([H.sub.v]= p V2/2g) are limited to 70 psi (4.8Bar).

[FIGURES 3-4 OMITTED]

In addition, each disk in these stacks incorporates a pressure-equalizing ring (PER) on its inside diameter to ensure equal pressure acting radially on the valve plug at all times to eliminate vibration that could occur because of rapid plug radial movement The propensity for rapid plug radial movement is undoubtedly one the principal causes of plug/guide galling in some valve designs.

These anti-surge recycle valves are designed with and ANSI Class VI plug-seat-redesign and materials to assure tight valve closure at shutoff. In this under-the-plug (flow-to-open) design, gas flow passes through the plug/seat-ring area under full compressor discharge pressure. The gas then enters the energy dissipating disk stack that is designed to accommodate changes in gas density from the expanding gas volume.

Actuators

To protect the compressors from severe damage in an upset situation, these anti-surge recycle valves must rapidly stroke from fully closed to fully open. A less than 1sec. stroking through 24 x 32 in. (600 x 900-mm) valve of 24 in (600 mm) full valve travel is achieved through low-volume actuators with quick exhaust valves on both sides of the pneumatic, double-acting actuator pistons, Fig 5. These actuators are supplied with 4.2 to 10.7 BarG (61 to 155 psig) air that is controlled by a 4 to 20 ma input signal to the positioner. Because a spring acts on the actuator piston, quick opening is assured in the event of power failure through properly sized volume tanks.

[FIGURE 5 OMITTED]

Atmospheric Flare And Other Valves

In addition to these compressor anti-surge recycle valves, 30 more similar control valves (again ranging up to 24 x 32 in. [600 x 900 MM]) for severe services, mostly at-mospheric flare control are in-corporated into these two latest LNG trains. For the same reason, i.e. a less-than 85 dBA with bare piping noise limitation, they too are of a multi-stage, tortuous-path trim design. However, in these applications, actuation speed is not as critical. Here 20 sec. is the specified maximum time limit for fully closed to fully open.

Depressurizing Valves

Also, some 34 depressurizing valves are involved. Since these operate rarely--emergency situation, etc.--their noise and operating speed requirements are far less stringent. Noise levels can go as high as 110 dBA with bare piping, and fully closed to fully open speeds of less-than 20 sec. are permitted. These drastically reduced operating requirements, of course, permit single-stage pressure reduction valves.

By Ricardo Simeoni, Industry Monitor NC O&G CCI, Rancho Santa Margarita, CA

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#5

Re: Use of Y type control valve

11/29/2008 12:47 AM

Hello saravanakumar761:

Dear All,

My question is I have seen a Y type control valve with pneumatic actuator in the LNG line of BOG Compressor

Are these the type of valves you were talking about? I know this is just sales 'patter', but when reading this does it make sense?

Hayward Flow Control Systems
Spring Loaded Y Check Valve

Hayward's Spring Loaded Y-Check Valves give positive protection against reversal of flow in a piping system, even in the absence of back pressure. Check valves that are not spring loaded require fluid back pressure to seal. If an application cannot produce enough back pressure, the standard check valve can't seal. (read more)

=============================================

Get back to me for more info and I will search for you.

Take care...........

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