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Monitoring And Control Components

Chemical and physical processes involving hydrogen íV like any hazardous materials - must be monitored to ensure that they are within specific control limits (safe operation window). Hydrogen production units and applications often require a rather complex control system, due to varying conditions and operation modes including significant dynamic operation. Examples of such conditions are given below

  • Variation in pressure and temperature between process sections
  • Variation in energy or raw materials supply
  • Varying power consumption/needs at application
  • Refuelling of vehicles
    • very high temperature and pressure variation in short time
    • many cycles
  • Atmospheric temperature variation

Hydrogen systems usually involve a considerable number of components, such as valves, pressure relief devices, pressure and temperature regulators, check valves, filters and instrumentation. These components are crucial for the safety of the system. The components in a hydrogen system must be fabricated of materials, including soft goods such as seats and seals, that are compatible with the operating conditions, and with each other if more than one material is involved.

The control system consist of measuring instrumentation - monitoring equipment such as flow meters, pressure and temperature transmitters, which in case of unacceptable process deviations will give a signal. This signal might give alarms in control room, or may initiate the control system e.g. to close or open valves dependent on the situation. Instrumentation provides a means to communicate with physical processes to obtain quantitative measurements of the behaviour or the state of the process. Controls provide a means to maintain or change the behaviour or state of a process. These are essential elements of a hydrogen system both for operation and safety of the system. It is of outmost importance that adequate instrumentation is designed so that the operation is within safe and acceptable limits.

Usually, when designing a hydrogen system a systematic analysis is carried out, to check out possible deviations from normal operating conditions. These deviations are identified by using keywords (high/low/no/reverse flow/pressure/temperature/ignition sources etc.). Causes and consequences of these deviations are identified, and in case a hazardous or otherwise unwanted consequence, systems for detection and control of the hazardous deviation are included in design of the system. Usually redundant systems are included for deviations that might lead to a hazardous situation.

Below some examples are given related to control components and situations when they are necessary. It must be underlined that this is just a very limited number of examples, and are not at all representative for the whole number of components or situations.

Examples of control components:

  • Regulation valves - for flow regulation and control.
  • Check valves - e.g. for prevention of reverse flow from a high pressure side to low pressure side.
  • Emergency shutdown (ESD) valves - to be closed in specific situations. These valves can be closed manually, by a push button at the site, from a remote control unit or automatically, for example by gas or fire detection signals. The activation is dependent on the control system and varies from installation to installation. ESD valves can for example be used to close the connection to a storage tank in case of a gas leak. They can also be used to isolate systems from each other. For example in case of gas detection inside a confined area, it might be recommended to have installed an ESD valve between storage and enclosure, to prevent the stored hydrogen go flow into the confined area.
  • Pressure relief devices - installed in process section/volumes in which hydrogen (liquid or gas) could be trapped. If the pressure reaches above a specific limit, these systems will open and ventilate the hydrogen to a safe location .

These components have to be approved for the environments/installations where they will be installed, e.g. by CE-marking in Europe. Also the operator/owner of the installation is obliged by various regulations to assure that the components are installed/used in accordance with theis speicifications and limitations.

Remote control of unmanned installations located in a public environment set high requirements to the control system íV to material properties and safe and reliable function.

These examples represent situations coupled to control of the "internal" process operation. In case of a hydrogen leak to atmosphere, additional systems might be necessary to lead the system to a safe condition. Examples of components and measures are gas detection, fire detection, emergency ventilation, deluge and sprinkling, explosion venting etc. These measures are described in chapter 5 on mitigation. Also in such situations a well designed process control system will bring the process to a so-called "fail-safe" condition, for example emergency shutdown of process, ventilation of hydrogen under pressure to a non-hazardous location and purging of process components with inert gas.

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Page last modified on December 19, 2008, at 01:03 PM