H2S Removal Using Scavengers
Posted on June 14th, 2021
Posted in Uncategorized
H2S is a well known, highly toxic contaminant that is found in some oil and gas production. Most H2S migrates to the gas, and removal is necessary to achieve sales gas pipeline specifications, or SO2 emissions limits. For applications with low levels of sulfur, the optimum method for removal is not always obvious. Owners often default to what is most familiar or most commonly applied, without considering other options available.
Scavengers offer a non-regenerable H2S treatment option that is typically reserved for applications with <500 lb/day of H2S, as operating costs and sometimes logistics often become impractical beyond this point. However, the economics of treating with scavengers are directly related to the sales price of gas and oil, the price of the scavenger, and whether the application is temporary or more permanent in nature.
There are both solid and liquid scavengers, both of which have their own advantages and disadvantages.
Liquid scavengers
While there are many liquid scavengers available, triazine is the most commonly used chemical for H2S removal. Controlled contact between triazine-based liquid scavengers and H2S is critical because excessive contact or high H2S concentrations can lead to saturation with dithiazine and precipitation. Solids formation is the most significant problem associated with the use of liquid scavengers.
Contact can be achieved in a variety to configurations. Less sophisticated contact mechanisms such as direct injection or static mixers are more likely to lead to chemical overuse and therefore higher operating costs and likelihood of plugging. Other more complex contact configurations such as batch contact towers or flooded tower systems allow better control of chemical use, though capital costs are higher.
Triazine based liquid scavengers do not react with CO2 therefore its presence does not negatively impact scavenging efficiency. Many formulations can partially remove light mercaptans (methyl, ethyl and propyl).
Solids formation and chemical overuse are the most notable problems associated with the use of liquid scavengers. Spent triazine solutions also have a very strong odor.
Caustic is another well known liquid scavenger. The challenge with caustic is that CO2 is also readily scrubbed by caustic, and conventional designs will generally scrub/remove most of the CO2 along with the H2S. The reaction of caustic with H2S is faster than that with CO2, so selective systems can be designed. In all cases, close attention much be paid to the solubility of the salts formed in the reactions with caustic. The composition of the salts is dependent on the presence of CO2, caustic strength, and solution pH.
Solid scavengers
The most inexpensive solid absorbents are based on iron chemistry. The oldest commercial form of this treatment is called iron sponge, which uses wood chips as a support material. One of the primary concerns about iron sponge was that the spent material is pyrophoric. This led to the development of many other iron-based solid scavengers that had a different substrate, which renders the spent material non-pyrophoric, amongst other improvements. There are now products offered that have no support material at all, which reduces the amount of material needed for treatment.
One of the primary concerns amongst users is related to the tendency of iron-based scavengers to agglomerate in the vessels over a period of time, making change outs labor intensive. Another limiting characteristic is that nearly all iron-based solid scavengers require the gas to be saturated with water, or at least have some water content; i.e., they cannot treat dry gas. Halker is aware of one iron-based product that claims to be able to treat dry gas, with the possible trade-off of reduced life.
There are also solid scavengers based on zinc oxide, copper oxide and mixed metal oxides. These solid scavengers do not rely on the presence of water, but they are also more expensive than iron-based absorbents and are therefore best suited for special cases, such as when the gas requiring treatment is dry or needs to be treated down to extremely low levels of H2S. In some applications with zinc oxide, it is possible to send the spent material to a smelter to recover the zinc and thereby reduce or eliminate disposal costs. Some copper oxide scavengers can be designed for simultaneous removal of H2S and mercury.
Finally, activated carbon can be used for H2S removal, though its application is typically limited to non-hydrocarbon streams because it will also remove hydrocarbons from gas streams.
If you would like to explore your options for H2S removal, our experts welcome the opportunity to to help you find the very best solution for your site.
Austin Dean graduated from Colorado School of Mines in Chemical and Biochemical Engineering. He has experience in engineering design projects for well pad facilities, gathering systems, and midstream natural gas facilities. Starting his career at Halker in 2014, his roles and responsibilities have spanned Process Engineering, Project Engineering, Project Management, and Facilities Engineering. He specializes in jet pump artificial lift surface facilities and dynamic hydraulic modeling. Austin brings an E&P perspective to the Halker team, with a focus on project economics and larger implications of design decisions.
Emily Strengers graduated from the University of Texas at Austin with a Bachelor of Science in Chemical Engineering in 1998 (Hookem’ Horns!). She has over (20) years of experience in the Oil & Gas industry, has been involved in projects ranging from offshore platforms to onshore crude units, LNG facilities, gas plants, cokers, and polyethylene units, and has worked in 6 different countries around the world. As a member of the Halker team since 2019, she has brought her extensive experience to aid in project management, client and staff training, FEED studies, construction support, and facilities operation for both upstream and midstream projects.
Jeff Wellen graduated from the Colorado School of Mines with a Bachelor of Science in Mechanical Engineering and a minor in business and economics in 2002. Jeff is a licensed professional engineer with over 19 years of project management, project engineering, and mechanical engineering experience. Most of his professional career has been in the Oil & Gas industry with a wide range of experience across various types of projects including gas treating, LNG, well pad sites, cryogenic processing, biofuels, and more. He has also worked as a field engineer to support construction, as well as in a fabrication shop to oversee module/pipe-rack assembly. As a member of the Halker team since January 2018, his breadth of involvement in various projects provides Jeff a strong basis to lead a project management team through the trials and tribulations when executing any type of project ranging from technical studies to full EPC projects in the rapidly evolving midstream and upstream industry sectors. Jeff was named an Engineering News Record (ENR) Top Young Professional in 2018 for the Mountain States Region.
Paul Brennan is an industrial automation specialist, PLC programmer, business manager and product development professional. He graduated from Colorado Mesa University in 1992 with a Bachelor of Science in Computer Science. Paul now has over 25 years of experience providing industrial automation solutions and large-scale automation integration projects for oil & gas, water/wastewater, irrigation, and greenhouse industries in the US and Eastern Europe. Paul’s career has been spent developing leading edge, revolutionary automation products, and in the process, he has obtained several US Patents. Paul has notably designed products such as PADPro, PADManager, PROView and QLogiX for upstream oil & gas facilities, utilizing state of the art technologies with PLC’s and high-powered single board computers to provide advanced data collection and data processing at the well head.
Jeremy Montoya graduated from the Colorado School of Mines with a Bachelor of Science in Engineering with an Electrical specialty focus in 2010. Jeremy is a licensed professional engineering in multiple states and has over a decade of experience in consulting engineering and has working in nearly every sector or the business, from oil and gas to food and beverage, mining, pharmaceuticals, commercial and residential applications. Jeremy started his own company, Selah Engineering and Design, in 2020 amidst the global pandemic and created a successful business that supported clients in a variety of sectors. Jeremy longed for a true multidisciplinary team through this time, which opened the door in 2021 for a partnership between Selah and Halker. In this partnership, Jeremy stepped into being the EI&C director at Halker, while continuing to support existing clients via Selah. As director, Jeremy brings a passion to build up and support staff as they provide quality engineering and design services to every client we have the opportunity to work with. With an eye for detail, value and confident support- our EI&C group will continue to grow and be recognized for their expertise, attentiveness, and quality deliverables in every project. Jeremy has also volunteered engineering services abroad, helping with the design of water/wastewater treatment facilities in Kenya, as well as master plans for facilities in Mexico.
Dan Grant has a Bachelor of Science in Electrical Engineering from Northern Arizona University. He is a licensed professional engineer in 22 states and brings over 30 years of experience to projects and clients. Dan completed his PMP and has worked as an engineer and project manager. His diverse career spans numerous market sectors, including energy, oil & gas (upstream, midstream, downstream, and water disposal processing), pipeline and terminals, mining (above ground and underground), chemical and pharmaceutical, water and wastewater and pumping stations, industrial manufacturing, clean rooms, 24/7 and mission critical operations, data centers and control facilities, and power (substations and transmission & distribution). In the renewable energy sector, Dan’s experience covers client-side and utility/grid-tied solar photovoltaic (PV) and concentrated PV power generation sites. At Halker, Dan previously served as the EI&C Director and now supports clients and projects as a team and technical resource. He’s knowledgeable in wide aspects of electrical design and engineering, including power system analysis, motors and VFDs, harmonics, grounding and bonding and lightning protection, cathodic protection, heat trace, relay protection schemes, electrical area classification and API RP500, and power generation.
Andrew Depperschmidt is a graduate from the Colorado School of Mines with a Bachelor of Science in Engineering Physics and a Master of Science in Mechanical Engineering. He has experience in a variety of construction and facilities projects including both upstream and midstream natural gas and crude oil processing. He joined Halker in January of 2015 as the Mechanical Department Manager and has since taken on several different responsibilities with the firm, including General Manager and Vice President. Over the course of his time with Halker, he has overseen the company’s growth, helped develop the management team, and helped structure operational processes around project execution for maximum quality. He’s inspired by Halker’s outstanding team daily and takes pride in being people-focused while driving the company’s progressive and forward-looking culture.