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Feb
12

Display content – part 1

Last week the topic was mobile. The discussion focused on different views such as display lists and alarm lists. These views provide the user with information specific to what they are interested in. In the last blog I said I would talk about display content.  To begin this discusstion I’ll start with a refinery and break the content down into units, common equipment, and finally to the most important parameters for each.

Let’s take a look at a refinery. The simple flow diagram below shows how crude oil is converted into higher-value fuel products. First, the raw crude is washed in a desalter and heated. Next, it enters the atmospheric crude fractionator, followed by the vacuum fractionator. These first units in a refinery involve no chemical reactions or catalysts; rather, based on each component’s boiling point, they separate and distribute the range of components for further downstream processing and conversion. Downstream units include such equipment as pumps and compressors, heat exchangers, reactors, and separation and distillation columns. Some of these downstream units contain a specific catalyst to convert the medium to a product with more desired qualities, and then separate it into intermediate products and off-gases. Finally, certain intermediate products from these units are blended into final products as per required specifications, such as octane and Reid Vapor Pressure (RVP) for gasoline.

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Looking more closely at this drawing, each unit (e.g. Crude Unit, Hydrotreaters, Coker, FCC, etc.) is largely made up of common processing equipment. For example, a Crude Unit is made up of Desalters, a Fired Heater, and a Fractionator. These are illustrated in the block diagram below.

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Each of this common processing equipment may be designed to include information that is specific to its operation, for example the Fired Heater may be represented on level 1 (L1) display with a limited set of parameters.

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Likewise, a Diesel Hydrotreater is made up of a Feed System, Heaters/Reactors, a Stripper, and a Gas Plant.

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The reactor may be represented on a L1 display as shown below (shown for a single or double reactor arrangement). Notice in this drawing that when we switch from one reactor two or more reactors it is usually better to use something like a table representation. The table representation provides a nice was to quickly see a summary of the two reactors.

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Users in the refinery have different spans-of-responsibility. For the example a specific operator may be responsible for one of the crude units and several diesel hydrotreaters. The span-of-responsibility should be summarized on a single L1 display. The L1display is further broken down into level 2 displays (L2) and level three displays (L3). The L1 displays provide overall situational awareness. The L2 displays are used by the operator for controlling the process. The L3 displays are used for investigation and debugging. Level 4 are purpose built displays, for example to start-up and shutdown the process. A good discussion on display levels is provided in ANSI/ISA-101.01-2015, Human Machine Interfaces for Process Automation Systems. Background information on display content is available through the Center for Operator Performance.

The next two blogs continue the discussion on content.