01
调节阀故障位置图例
SH/T 3101-2017 石油化工流程图图例
4 图例
4.8 调节阀故障位置
02
常用阀的气开,气关式如何选择?
某工程工程设计规定举例(1996年):
调节阀气开、气关式选择规定
总则:调节阀气开、气关式的选择应满足在控制信号或气源故障时,调节阀的阀位使工艺操作处于安全状态,以免设备损坏和人员伤害。
一般常用阀的气开,气关式选择如下:(但最终由工艺确定)
1、加热炉燃料油、燃料气调节阀应用气开式。
2、加热炉被加热的物料调节阀宜用气关式。
3、汽包蒸汽出口调节阀应用气关式。
4、汽包给水阀应用气关式(或附加保险阀)。
5、压缩机入口调节阀应用气关式。
6、压缩机旁路调节阀宜用气关式。
7、压缩机出口压力调节放空阀宜用气关式。
8、分馏塔进料流量调节阀宜用气开式。
9、分馏塔回流量调节阀宜用气关式。
10、重沸器加热流体调节阀宜用气开式。
11、分馏塔顶压力调节阀宜用气关式。
12、塔、釜的排料调节阀宜用气开式。
13、换热器被加热流体出口温度过高会引起分解,结焦时加热流体调节阀宜用气开式。
14、换热器被加热流体出口温度过低会引起结晶,凝固时加热流体调节阀宜用气关式。
15、贮罐压力调节系统的调节阀宜用气关式。
16、贮罐液位调节系统:
a) 当调节阀装在入口管线时宜用气关式。
b) 当调节阀装在出口管线时宜用气开式。
17、蒸汽、燃料气等总管分配至装置界区内支管上的压力,调节阀宜用气关式。
18、无弹簧活塞式执行机构,气源中断时为使调节阀能处于安全极限位置,可设置带贮气罐的专用保护系统,如需要保持在原有的工作位置,应设置闭锁阀。
注意:以下仅为举例,不代表所有情况,仅为某些情况、场景的举例,具有适用的限制性。
03
1、阀门通常会有一个安全位置,关闭(FC)或者打开(FO)。
2、阀门安全位置为关闭(FC)的情况居多,因为将一个部分隔离,与其他环节隔离为通常的安全状态,所以,阀门安全位置为关闭(FC)的情况居多。
3、隔离,不将局部的危险传递到下游通常是安全的,这样一个部分,入口和出口安全位置通常定义为关闭(FC)。
4、一个部分的内部,安全的状态是,控制好温度和压力,为此,用于压力泄放(降低系统压力)的阀门安全位置通常为打开(FO);温度控制,用于提供热源的(比如重沸器、取热等),通常安全位置为关闭(FC);温度控制,用于提供冷源降温(比如空冷器等),通常安全位置为打开(FO)。
5、泵罐隔离,最终的安全位置通常为关闭(FC),为了一定程度上可以尽可能的不影响生产,可以采用FLC,配置储气罐。
6、高压加氢紧急泄压,安全位置通常为打开(FO),为了一定程度上减少对工艺过程(包括反应器内件、火炬管网等)的影响,可以采用双路紧急泄放,低速泄放采用FO,高速泄放采用FC,并且配置储气罐,并采用双电磁阀(两个电磁阀都失电,才执行联锁)用于提高可用性。
7、装置内部介质之间的换热器,由于是介质温度互相交换,并不减少总热量,换热器旁路通常采用FO。加热炉通常不设置旁路,安全位置为关闭(FC),故障时,加热炉不再加热介质。
8、空冷器等为取热,可以降低系统热量,为安全状态,空冷器等旁路通常采用FC,故障时,走空冷,尽可能多的取热,利于温度降低,增加安全性。
9、很少有绝对的FL需求,通常都是FLC或者FLO,通常会有一个安全位置,保位为暂时需求,是为了尽可能的不影响工艺过程的连续操作。FLC和FLO工艺通常要求配置储气罐。
工程实际的问题:控制阀FC/FO和工艺联锁方向一致时(例如:FC控制阀联锁方向为关闭阀门,FO控制阀联锁方向为打开阀门),F可以认为失气和信号中断。可以设计成电磁阀失电执行联锁。
控制阀FC/FO和工艺联锁方向一致时(例如:FC控制阀联锁方向为打开阀门,FO控制阀联锁方向为关闭阀门),此时情况复杂一些,这时没有绝对的安全的方向,不论是阀门关闭或者打开,都有其优点和缺点,这时采用电磁阀失电联锁还是采用电磁阀得电联锁,需要根据工程实际确定,包括标准规范要求、设计统一规定要求、工艺安全考虑、安全性和可用性考虑、误停车经济损失等情况。
拓展知识
API RP 553-2012 Refinery Valves and Accessories for Control and Safety Instrumented Systems
3 Terms and Definitions
3.11 fail-closed
A condition where-in the valve closure member moves to a closed position when the actuating energy source (air or signal) fails or is lost.
3.12 fail-open
A condition where-in the valve closure member moves to a open position when the actuating energy source (air or signal) fails or is lost.
3.13 fail-safe
A characteristic of a valve and its actuator which upon a loss of actuating energy supply (air or signal) will cause a valve to move to be fully closed, fully open, or remain in its last position, whichever position is defined as necessary to protect the process.
4 Control Valves
4.3 Valve Actuators
4.3.6 Actuator Selection
4.3.6.3 Valve failure position should be carefully analyzed in the event that supply pressure or instrument signal is lost. Generally, the valve should fail in the safe direction on loss of power or signal.
4.3.6.4 The most reliable fail-safe action is achieved with an enclosed spring. If volume tanks are required to provide reserve operating power, they should be sized to stroke the valve twice. Volume tanks should be stamped and otherwise conform to ASME Code guidelines (see Part U-1, Section VIII, Division 1, ASME Boiler and Pressure Vessel Code). Volume tanks should be designed with all necessary accessories to ensure the required valve action and failure position.
7 Refinery Applications
略
某工艺包的定义
注意:以下定义并不是唯一的,不同项目、不同标准可能有不同的定义,例如:FC、FO中的F,有的代表气源故障和无信号,有的只代表气源故障而不包括无信号。
FC,FAIL CLOSED (VALVE TO CLOSE ON AIR OR ELECTRICAL FAILURE)
FO,FAIL OPEN (VALVE TO OPEN ON AIR OR ELECTRICAL FAILURE)
FL,FAIL LOCKED (LAST POSITION)
FLC,FAIL LOCKED (AIR FAILURE) CLOSED IN CASE OF SIGNAL FAILURE
FLO,FAIL LOCKED (AIR FAILURE) OPEN IN CASE OF SIGNAL FAILURE
LO,LOCKED OPEN
LC,LOCKED CLOSED
PIP PCCCV003-2017 Remotely Actuated On-Off Valves Selection Criteria
3. Definitions
fail-safe: Characteristic of a particular valve and its actuator that,upon loss of actuating energy supply,causes a valve closure member to be fully closed, fully open,or remain in the last position,whichever position is defined as necessary to protect the process. Fail-safe action may involve the use of auxiliary controls connected to the actuator.
PIP PCECV003-2017 Guidelines for Application of Remotely Actuated On-Off Valves
7. Actuators
7.3 Failure Position
7.3.1 Failure position is an important consideration for remotely actuated on-off valves. Failure position, also called failsafe position, is the action of the valve upon failure of motive force (e.g., instrument air) or loss of signal (e.g., signal to the solenoid valve). The failure action of the valve should be evaluated based on the valve’s effect on the operation of the process. The valve should be designed to fail to the position that would result in a safe process condition which should be determined based on a broad overview of the process plant operation.
7.3.2 Failure position may be open, closed, last position or indeterminate.
7.3.3 For detailed definitions see PIP PIC001.
PIP PIC001-2008 Piping and Instrumentation Diagram Documentation Criteria
3. Definitions
fail closed (FC): Characteristic of an automated valve that causes the valve to close as a result of specific malfunctions, including loss of signal or motive power. (Reference ISA 5.1)
fail indeterminate (FI): Characteristic of an automated valve that causes the valve to move to an unknown position as a result of specific malfunctions, including loss of signal or motive power. Some automated valves will not stay at the last position upon failure and instead move with the process differential pressure. Additional equipment may be needed to meet the definition of FC, FO, or FL. (Reference ISA 5.1)
fail locked (FL) last position: Characteristic of an automated valve that causes the valve to remain in the last (locked) position as a result of specific malfunctions, including loss of signal or motive power. Automated valves may fail indeterminately without additional equipment. (Reference ISA 5.1)
fail open (FO): Characteristic of an automated valve that causes the valve to open as a result of specific malfunctions, including loss of signal or motive power. (Reference ISA 5.1)
DEP 32.36.01.17-Gen. CONTROL VALVES - SELECTION, SIZING, AND SPECIFICATION
8. SPECIFICATION OF CONTROL VALVE ACTUATOR
8.1.1 Spring action
Spring-to-open and spring-to-closeare fail-saferequirements which shall be determined by process engineering and which shall be indicated on the PEFS. If no particular fail-safe action is required the position of the valve can either be fail last (stay-put) or floating. Fail last(stay-put) means that devices are in place to retain the position the valve had at the moment when the supply failed. Floating means that the position of the valve is determined by the balance of forces acting on the plug and the actuator (the final position is undetermined). This choice shall be indicated in the requisition (IEC 60534-7:2010, line 29).
Double acting actuators without spring shall not be used on applications that require operational adjustments of the valve in case the plant air supply is lost unless the required fail-safe action can be achieved by a pneumatic supply buffer vessel.
《过程控制》
清华大学出版 金以慧主编<过程控制>
“阀气开/气关形式选择原则主要从工艺生产的安全出发。当仪表供气系统故障或控制信号突然中断,调节阀阀芯应处于使生产装置安全的状态.”
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