# Process Flow Diagram Symbols for Chemical Engineering Canonical: https://sakura5.app/blog/procss-flow-diagrams-symbol-ceme/ Published: 2026-11-07 Author: the Sakura5 team · 8 min read Updated: 2026-11-07 Publisher: Sakura5 (https://sakura5.app) · support@sakura5.app > **TL;DR:** Process flow diagram symbols for chemical engineering: vessels, pumps, columns, exchangers, tags and stream numbers, plus a full distillation PFD example. ![Process Flow Diagram Symbols for Chemical Engineering](https://sakura5.app/img/blog/inline/procss-flow-diagrams-symbol-ceme-1.jpg) Process flow diagram symbols in chemical engineering are a small, standard set of equipment pictures: a tall capsule for a column, a rounded drum for a vessel, a circle with a tangential outlet for a pump, a trapezoid for a compressor, a circle crossed by a line for a heat exchanger, a bowtie for a valve, and heavy arrowed lines for the process streams that connect them. Each piece of equipment also gets a tag such as P-101 or E-102, and each stream gets a number that points to a table of flows, temperatures and pressures. If you came here from a business flowchart, this is a different language. A chemical engineering PFD shows a plant, not a procedure. The shapes are meant to look roughly like the equipment they stand for. This guide covers why PFD symbols trip people up, the symbols you’ll actually need with what each one means, the tagging and stream-numbering conventions, a worked example of a small distillation unit drawn from scratch, where a PFD ends and a P&ID begins, and the questions students ask most. ## Why process flow diagram symbols confuse people The first problem is the name. In business, a “process flow diagram” is a flowchart of steps and owners, and most search results mix the two together. If you are a chemical engineering student and the first chart you find is full of ovals and diamonds, you are looking at the wrong notation. Our guide on [how to make a process flow diagram](https://sakura5.app/blog/how-to-make-a-process-flow-diagram/) covers the business version; this one is about plants. The second problem is that there is no single universal symbol sheet. ISO 10628 defines graphical symbols for flow diagrams of process plants, many companies follow their own drafting standard, and textbooks each draw a pump or heat exchanger a little differently. A beginner sees three versions of a heat exchanger and assumes they mean three different things. The third problem is level of detail. Students often try to draw every valve, drain and instrument on a PFD. That belongs on the piping and instrumentation diagram. A PFD is deliberately simplified so you can see the whole process on one sheet. ## The core process flow diagram symbols and what they mean These are the symbols that cover most undergraduate design projects and most real PFDs. ![The core process flow diagram symbols and what they mean — process flow diagram symbols](https://sakura5.app/img/blog/inline/procss-flow-diagrams-symbol-ceme-2.jpg) *These are the symbols that cover most undergraduate design projects and most real PFDs.* ### 1. Vessels, drums and tanks A vessel is drawn as a rectangle with rounded or elliptical ends, vertical or horizontal depending on how it sits in the plant. A storage tank is usually drawn with a flat bottom and a flat or cone roof, because that is what an atmospheric tank looks like. ### 2. Columns and towers A distillation, absorption or stripping column is a tall, narrow vessel. Many drafting styles add dashed lines for trays and show the feed entering partway up the side. ### 3. Pumps and compressors A centrifugal pump is a circle with the discharge line leaving tangentially from the top. A compressor is usually a trapezoid that narrows from the suction side to the discharge side, a picture of gas being squeezed into a smaller volume. ### 4. Heat exchangers, heaters and coolers The simplest heat exchanger symbol is a circle with a line or zigzag passing through it, showing one stream exchanging heat with another. ### 5. Reactors A reactor is drawn as a vessel, typically with an agitator shaft and blades if it is a stirred tank, or packed and jacketed if it is a fixed-bed or cooled reactor. ### 6. Valves, lines and instruments A basic valve is a bowtie: two triangles meeting at their points. A control valve adds an actuator, usually a dome or small rectangle on top. Main process streams are heavy solid lines with arrows showing direction; utilities such as steam and cooling water are lighter lines. Instruments appear as small circles, or bubbles, with a tag such as FIC for a flow-indicating controller, and a PFD shows only the main control loops. ## Tags, stream numbers and the stream table A common scheme, used in widely taught design textbooks, gives each equipment type a letter and each plant area a hundreds number: P-101 is the first pump in area 100, E-102 the second heat exchanger, T-101 a tower, V-101 a vessel, R-101 a reactor, C-101 a compressor. Companies vary the letters, so always check the legend on the drawing. Each process stream gets a number, usually written inside a small diamond or flag on the line. Those numbers key into a stream table at the bottom of the sheet listing flow rate, temperature, pressure, phase and composition for every stream. The general layout is summarized well in the [overview of process flow diagrams on Wikipedia](https://en.wikipedia.org/wiki/Process_flow_diagram). ## A worked example: a methanol–water distillation unit Say your design assignment is a small unit that separates a methanol–water feed into a methanol-rich top product and a water-rich bottom product. The brief gives you a feed of 1,000 kg/h from a storage tank at 25 °C. ![A worked example: a methanol–water distillation unit — process flow diagram symbols](https://sakura5.app/img/blog/inline/procss-flow-diagrams-symbol-ceme-3.jpg) *The brief gives you a feed of 1,000 kg/h from a storage tank at 25 °C.* ### Step 1: list the equipment before drawing anything Read the brief and pull out every piece of equipment it implies: a feed tank, a feed pump, a feed preheater, the column, an overhead condenser, a reflux drum, a reflux pump, a reboiler, and two product coolers. That is 10 items. A mind map is handy at this stage because you can branch “Distillation unit” into “Feed section,” “Column,” “Overhead” and “Bottoms” without committing to a layout. In [Mindmap AI](https://sakura5.app/mindmapai/), a Pro subscriber can paste the assignment brief and get a starting map of its parts, then correct the branches instead of starting from a blank page. ### Step 2: assign tags Using the area-100 scheme: TK-101 feed tank, P-101 feed pump, E-101 preheater, T-101 column, E-102 condenser, V-101 reflux drum, P-102 reflux pump, E-103 reboiler, E-104 distillate cooler, E-105 bottoms cooler. ### Step 3: trace and number the streams Follow the material from the tank to the products and number each line as you go. Stream 1 leaves TK-101, stream 2 leaves P-101, stream 3 leaves E-101 and enters T-101 at the feed tray. Stream 4 is the column overhead vapour to E-102, stream 5 the condensed liquid to V-101, stream 6 the reflux returned to the top tray, and stream 7 the distillate to E-104. Stream 8 is the column bottoms, split into stream 9 to E-103 and back as boil-up, and stream 10 to E-105. You end up with 10 numbered process streams, not counting steam and cooling water. Mindmap AI’s outline view shows the same map as an ordered, collapsible list, which is a quick way to check that every stream has a source and a destination. ### Step 4: draw it with the standard symbols Lay the drawing out left to right in the direction of flow: tank, pump circle, exchanger circle, then the tall column in the middle. Put the condenser and reflux drum beside the column top, the reboiler at the bottom, and the coolers on the right edge. Draw process lines heavy, utilities light, and add only the main control loops: a flow controller on the feed, a level controller on the reflux drum, and a temperature controller on the reboiler steam. ### Step 5: fill the stream table and check the balance Add a column to the stream table for each of the 10 streams. The quickest sanity check is the overall mass balance: stream 7 plus stream 10 must equal the 1,000 kg/h in stream 1. If your distillate is 300 kg/h, your bottoms must be 700 kg/h. If they do not close, a stream is missing or double-counted. ## PFD vs P&ID: where the symbols stop A PFD answers “what does this plant do and how much flows where?” A piping and instrumentation diagram answers “exactly how is it built and controlled?” The P&ID adds every valve, line size, instrument, alarm, drain, vent and relief valve. A good rule: if removing a symbol would change the mass or energy balance, or hide a major control loop, it belongs on the PFD. If it only matters for construction, maintenance or safety detail, move it to the P&ID. For a side-by-side look at how symbols change between notations, see our guide to [flow diagram symbols examples](https://sakura5.app/blog/flow-diagram-symbols-examples/). If you are revising for an exam, the equipment list, tags and stream route from the example above make a tidy map to review. [Mindmap AI](https://sakura5.app/mindmapai/) can export a map as a PDF outline on Pro, which turns the inventory into a one-page checklist you can test yourself against. ## FAQ **What are the main process flow diagram symbols?** The main chemical engineering PFD symbols are vessels and drums, storage tanks, columns, pumps, compressors, heat exchangers, reactors, valves, process lines and instrument bubbles. Each item also carries an equipment tag such as P-101, and each process line carries a stream number that links to the stream table at the bottom of the drawing. **Is there a standard for process flow diagram symbols?** Yes. ISO 10628 defines graphical symbols for flow diagrams of process plants, and many companies base their drafting standards on it or on their own internal symbol legend. Shapes vary slightly between companies and textbooks, so a professional drawing always includes a legend sheet that explains the symbols and tag letters it uses. **What is the difference between a PFD and a P&ID?** A PFD shows the major equipment, the main process streams, key control loops and a stream table of flows, temperatures and pressures. A P&ID shows how the plant is actually built: every valve, line size, instrument, alarm, drain, vent and relief device. The PFD comes first, and the P&ID is developed from it. **How do I remember PFD symbols for an exam?** Learn each symbol as a picture of the real equipment: a tall capsule is a column, a narrowing trapezoid is a compressor squeezing gas, a circle with a tangential outlet is a pump. Then practise on one complete unit, such as a distillation column with its condenser, reflux drum and reboiler, labelling every tag and stream number. 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