CHEMICAL INJECTION METHODS Pros & Cons 1
Chemical injection is an integral component of any pipeline integrity program. The petroleum, chemical, and water treatment industries require chemical treatments to control various undesirable contaminants and prevent asset degradation. Some of the chemicals typically injected are corrosion, scale, and paraffin inhibitors; hydrogen sulfide, carbon dioxide and oxygen scavengers; biocides; glycols and methanol. Careful consideration of the injection method chosen will provide a cost effective and reliable solution. Criteria required to select the proper chemical injection method: 1) The treatment required and chemical selected 2) Process conditions a. Process Fluid (i.e. natural gas, crude oil, water, etc.) b. Pressure (min-normal-max) c. Temperature (min-normal-max) d. Flow rate (min-normal-max) e. Process density 3) Chemical density relative to water 4) Injection site specifics a. Pipeline diameter or vessel size b. Injection port size and type c. Utilities to power pump 2
A typical chemical injection system: 1) Chemical bulk tank constructed of materials compatible with the chemical and sized adequately to minimize refilling 2) Spill containment reservoir sized to hold 1.5 2 times the storage tank contents 3) Chemical strainer/filter (80 mesh) for larger particulate removal 4) Gauge to set the pump discharge rate 5) A positive displacement pump capable of pumping pressures well above maximum process pressure; *materials of construction compatible with the chemical A. Diaphragm or piston actuated pneumatic a. Natural gas instrument supply requires instrument supply regulator, filter dryer, and lubricator. b. Instrument air supply B. Electric motor actuated a. 240 VAC or 120 VAC supply must consider electrical area classification b. 12 VDC solar and battery sized for winter temperatures and lack of sunshine 6) Pump discharge pulsation dampener constructed of materials compatible with chemical 7) Nipple, quill, or atomizer with 50 micron inlet filter, check valve, pressure gauge, and isolation valve *An adjustable relief should be plumbed from the pump discharge to the pump suction for over pressure protection. 3
4
Characteristics of Various Chemical Treatments: 1) H2S, O2, and CO2 scavengers* A. Densities similar to water and must be dispersed and distributed thoroughly within the process media for maximum contact time. B. Requires continuous direct injection distributed via an atomizer. 4) Corrosion inhibitors * A. Density similar or slightly heavier than water and is applied to the interior wall of the pipeline or vessel. B. Requires continuous or batch injection distributed via a nipple with check valve. 5) Paraffin inhibitors in crude oil A. Densities slightly lighter than water and must be dispersed and distributed thoroughly within the process media for maximum contact time. B. Requires continuous or batch injection distributed via a quill with check valve. Static mixers may be considered if pressure drop can be tolerated. 4) Glycols A. Density slightly heavier than water and is applied to the interior wall of the pipeline or vessel. B. Requires continuous or batch injection distributed via a quill with check valve. 5) Methanols A. Densities slightly less than water and must be dispersed and distributed thoroughly within the process media for maximum contact time. B. Requires continuous direct injection distributed via an atomizer. * Injection quills should be used when distributing chemical in a liquid media. 5
There are numerous pump styles available, but they all have common components. 1) Actuation Motor A. Pneumatic a. Natural Gas b. Instrument air B. Electric a. 240 VAC or 120 VAC (Area Class) b. 24 VDC Batteries with Solar Panel 2) Pump a. Piston b. Plunger d. Diaphragm e. Bellows 3) Packing/Seals compatible with chemical 4) Air Bleeders 5) Inlet and Outlet Check Valves 6) Rate Adjustment a. Stroke Length b. Timer 6
Information required to choose the correct pump: 1) Size the pump for the full range of injection rates required. 2) Size the pump for discharge pressures well above process pressures plus any restrictions within the chemical injection system. Example: Process pressure of 800 psi and spring loaded nozzle cracking pressure of 425 psi. The pump must be capable of pumping pressure s above 1225 psi. 3) Method of pump actuation a. Clean dry instrument supply gas a. Natural Gas (consider emissions, poor gas quality) b. 240/120 VAC Electric (subject to power outages) c. 24 VDC solar and battery (consider lack of sunshine, battery disposal) 4) Durability a. Materials of construction must be compatible with the chemical. b. Undersized pumps must be stroked at their maximum range. 7
Pulsation dampeners are a valuable addition to any well-designed chemical injection system. Pulsation dampeners are used to decrease pressure spikes in the pump discharge as well as becoming a secondary pump. The pulsation dampener contains compressed stored energy which discharges with the back stroke of the pump. Ultimately, the pump stroke time can be slowed down reducing valuable wear and tear. The bladder style pulsation dampener is better suited to the challenges of a continuous pipeline injection system. 8
Choosing the appropriate chemical distribution method. 1) Is the process fluid a gas or liquid? A. Gas a. Requires an insertable atomizer for most chemicals.* b. Quill can be used if velocity is greater than 15 ft/second. c. Nipple with check valve should be used for corrosion inhibitors. B. Liquid a. Requires an injection quill for most chemicals.* 2) Does the chemical require distribution and dispersion for maximum contact throughout the process fluid? a. Requires an insertable atomizer.* 3) Is the chemical required to coat the pipeline or vessel walls? a. Requires a nipple and check valve. 4) Is the chemical required to target a specific undesirable with a specific location within the pipeline of vessel (i.e. water in crude oil)? a. Requires a quill to the bottom of the pipe or a bottom injection with a nipple and check valve.* *Insertable probes within a liquid process and a gas process with excessive velocity are susceptible to bending and frequency oscillations which may cause stress failures. Probe stress calculations are suggested when in doubt. 9
Choosing the appropriate chemical distribution method (part 2). 1) What are the design and operating pressures and temperatures? A. Can a hand insertable atomizer or quill be used? B. Is a mechanically insertable atomizer or quill required? 2) What is the process fluid velocity and density? Is a probe stress calculation required? Need process velocity, density, and temperature. 3) What is the pipeline diameter or vessel size? What is the insertion length required to injection zone? 4) What is the access port size and type? A. If insertable atomizer or quill is desired a full port process isolation ball valve is required. Ball valve size and type connection (i.e. 1/2-2 NPT or flanged) B. If fixed quill is desired. Size and type of port (i.e. 1/2-2 NPT or flanged) 10
11
The nozzle is the key component of an injection atomizer. Sizing and selection is based on several factors. 1) Injection rates (min-max) 2) Density of chemical 3) Pump discharge pressure capability 4) Process pressures (min max) A 50 micron filter, check valve, and pressure gauge is a must when using an atomization nozzle. 12
Conclusion Chemical injection is not merely an after thought. Rather, it takes considerable planning for a safe, reliable, and efficient system! 13