What is a Chemical Injection Quill? (PDF)

The injection quill is a precision-engineered mechanical device. As this device is widely used in the chemical injection process it is popularly known as the chemical injection quill. Various chemical industries use injection quills to provide an effective and safe means of injecting liquid chemicals into a vessel or pipeline system. They are usually a part of metering systems.

Applications of Chemical Injection Quills

Injection quills dose the chemical into the interior section of the flow and thereby keeping the chemical away from the sidewall and fittings. Chemical injection quills serve as an interface between the chemical feed line and the processing pipeline. The quill delivers the chemical efficiently into the interior of a process pipeline flow. Various chemical industries make use of chemical injection quills in applications like additive injection, bio-treatment, chemical injection, removal and separation processes, etc.

Types of Chemical Injection Quills

To meet the demand for handling various chemical substances, there are a wide variety of injection quills that are found in industrial applications. All these chemical injection quills are categorized into one of the following two types:

Retractable Quills allow the operator to retract the injection quill without fully depressurizing the vessel or pipeline. These types of injection quills are complex in design and highly beneficial for clog-prone systems requiring frequent maintenance but where frequent shutdown is not feasible.

All retractable injection quills have the following components:

• Solution Tube that carries the treatment chemical.
• Restraint system to keep the solution tube in place.
• Isolation valve assembly consists of a valve and compression gland.

Non-Retractable Quills where the vessel or pipeline must be depressurized to remove the chemical injection quill. Non-retractable types of injection quills are widely used for chemical systems that do not form frequent deposits to clog the quill.

Depending on the number of Ports, injection quills are classified as follows:

• Dual Port Injection Quill: These types provide a uniform and rapid dispersal of two chemicals injected into one port.
• 3-port Injection Quill: Deaerators, boilers feed water tanks, etc use this type of injection quill for more uniform and rapid dispersal of chemicals into the center of the process pipe.
• 4-port Injection Quills: These are specially designed injection quills to disperse four chemicals into one port.

Chemical Injection Quill Configurations

Industrial injection quills are manufactured in various configurations, connections, and fittings. The configuration varies from a simple fabricated tube/probe to an integrated assembly with isolation valves and non-return valves. A compact integrated assembly consisting of the chemical injection quill, probe, double block & bleed assembly, and an integral non-return check valve is always beneficial.

Injection quills can be used as sampling quills by redesigning the probe and removing the integral check valve to safely take out fluid samples from the process line.

Chemical injection quills are mounted into the pipeline through a fitting. The probe is inserted and extended to the center of the process line. The other end of the injection quill connects to the chemical feed line by a pipe or tubing connection.

Designing An Injection Quill

The design of an injection quill is governed by various parameters like:

Design calculation

The wake frequency is calculated following the guidelines provided in the ASME PTC 19.3 TW standard for Thermowell as the injection quill is similar to it. The design of chemical injection quills needs both thermal and stress considerations. So process parameters like fluid, temperature, pressure, velocity, flow rate, density, viscosity, etc must be known for designing the injection quill.

Material of Construction

The material grade of the injection quill is selected such that the material is suitable for the service and the chemical to be injected. As the quill forms an integrated assembly together with the DBB and the check valve, several parameters similar to an isolation valve design must be evaluated.

Dimensions

The length of the injection quill is one of the most important parameters for wake frequency calculation. The length can be customized. Bore Size, Insertion Length, Tip Diameter, Root Diameter, Overall length, etc are the important dimensions to be considered during design.

Nozzles

In general, cylindrical tubes or nozzles are used for injection quills. However, specially designed nozzles depending on the application can be designed.

Mounting options

The design of injection quills can vary based on mounting options. Various different mounting options like flanged, welded, or threaded are possible. However, the quill/probe outside diameter (O.D.) must fit all the way down to the process stream.

Selection of Injection Quills

The selection of required injection quills depends on the following factors:

• Retractable or Non-Retractable
• Key dimensions like solution tube size, process connection size, insertion length, pressure class rating, etc.
• Materials of Construction required.