Flowmeters for Chemical Injection
Most engineers know that chemical injection is the process that assists in the production of oil. To provide a degree of protection, various chemicals are injected into the crude oil. For instance, a scale inhibitor will prevent the build-up of scale on the fittings, as well as the pipes used to transport the oil during its journey to the refinery. To control and monitor the amount of chemicals that are added to the crude oil, flowmeters are used. Biocide prevents the
buildup of organisms inside the pipe, while the depressant is added to reduce the pour point and make the oil flow easier through the main pipelines. The most popular additive to be measured with a flowmeter is a corrosion inhibitor and, depending on the main liquid, there are various types that can be used. Most chemicals are supplemented at a low flow rate of 0.0-1 to 40 liters per hour. On the other hand, the highest injection rate is the Low Dosage Hydrate Inhibitor (LDH), which sometimes goes up to 17,000 liters per hour. The LDH is designed to inhibit water-based mixtures that would otherwise have a tendency to freeze. Methanol is used often with the same effect. For the intention of reducing cost on the way to the refinery, more exotic chemicals are used for similar purposes. Many people do not know that flowmeters are, in fact, used to measure these chemicals. These chemicals contribute about 30% of the cost of running an offshore platform. There is a trend towards automation of chemical injections using control valves such as SkoFlo. As of now, control systems are often manually set from the flowmeter locally or from the SCADA system.
With some Positive Displacement flowmeters, a typically turndown ratio of 500:1 is obtainable. The system is slow and that’s why it is still easy to control manually – it’s not the other way around. Manual control is still popular; the system often needs slight adjustments from day-to-day, because it is dynamically relatively slow. It is very important that the flow measurement system is able to cope with the high pressures that are encountered and the pulsing nature of the pumps used. In modern systems injecting subsea, these can be up to 1035bar/15000psi/15ksi. At lower pressures, the topsides injection is typically from 200 to 1,000 psi. Rather than measuring when the crude oil reaches the surface, there is a trend towards measuring the chemicals subsea. The flowmeter has to work not only at high internal pressures of over 10,000 psi/690bar, but also up to 345bar/5,000psi external pressures. All of the details on the flowmeters suitable for chemical injection offered at JLC International can be found at https://jlcinter.wpengine.com/flowmeters/chemical-injection. We offer the Rotary Piston Positive Displacement Flowmeters Series VFF and Instrumentation for Flow Rate and Totalizing.