Air Pollution Control Innovations

Andy Olds

Engineering Manager at Envitech
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Recent Posts

Mobile NOx Packed Bed Scrubber for Sulfuric Acid Manufacturers

Posted by Andy Olds on Thu, May 17, 2018 @ 01:00 PM

Sulfuric acid plants manufacture acid by burning sulfur with air in a smelter to form sulfur dioxide (SO2), oxidizing sulfur dioxide catalytically into sulfur trioxide (SO3), and absorbing sulfur trioxide into water to form sulfuric acid.  An unwanted coproduct of sulfur combustion is nitrogen oxide (NO).  In the catalyst beds, nitrogen oxide partially converts to nitrogen dioxide (NO2) and the two react with sulfuric acid to form nitrosylsulfuric acid (NOHSO4).  Candle filters located downstream of the catalyst beds collect most of the nitrosylsulfuric acid.Vertex_Rectangular_Scrubber

Candle filters require periodic maintenance. To maintain the equipment, operators wash the candle filters with water to remove the sulfuric acid contained within them before entering the candle filters for maintenance activities. Unfortunately, water reacts with built-up nitrosylsulfuric acid to reform NOx. Since there is no diluting gases, NOx concentrations leaving the candle filter during the wash may be very high, both dangerous to operators and potentially forming an opaque brown cloud.

Recently, Envitech developed an economical solution to this problem by designing a mobile NOx scrubber. A mobile NOx scrubber, rather than a fixed system, has several advantages in this application. First, a mobile system does not consume valuable footprint during normal operation. The area around the candle filters is often congested. A fixed system requires "shoe-horning" the equipment in a hazardous location, adding cost. A mobile solution provides flexibility to position the scrubber in optimal locations near the candle filter without permanently consuming valuable space. Temporary utility connections suffice for a mobile solution, further reducing installation costs. Second, a mobile scrubber can service multiple candle filters or other process vessels, even at different facilities. Finally, Envitech's mobile scrubber is multi-functional, designed to abate a number of hazardous chemicals in addition to nitrosylsulfuric acid, such as hydrochloric acid, sulfur dioxide, and other soluble gaseous emissions.

Envitech's mobile NOx scrubber offers the ability to abate over 99% of the NOx emissions during maintenance activities for flow rates of up to 1,000 acfm for a single reagent system and 15,000 acfm for a multi-reagent NOx reduction system. Envitech's mobile NOx scrubbers are fully automated, stand-alone scrubbers requiring only utility and gas connections, and configurable to handle a variety of pollutants. If you are interested in more information about Envitech's mobile scrubber, click on the link below to download a cut sheet for the scrubber.

Download Cut Sheet

Topics: Scrubbers, NOx

Ethylene Amine Scrubber

Posted by Andy Olds on Mon, Jul 10, 2017 @ 03:20 PM

Vent Scrubber.jpgEthylene amines are one of the major chemical building blocks.  Ethylene amines include ethylenediamine (EDA), diethylenetriamine (DETA), triethyltriamine (TETA) as well as other longer chained ethylene amines.  Amongst its many uses, ethylene amine is one of the two principal chemical ingredients in making ethylenediaminetetracetic acid (EDTA), the most common chelating agent in the world.  Diamines are also used in the manufacture of the ubiquitious textile Nylon. Due to its excellent properties, it is also used extensively in the asphalt, petrochemical, rubber, pesticide, and paper industries.

The storage of this precursor chemical requires extra handling than is typical with other common industrial chemicals.  Ethylene amines possess relatively low OSHA exposure limits of 10 ppm or less and have a vapor pressure akin to water; thus vent points in ethylene amine storage systems must be properly engineered to avoid hazardous conditions, and scrubbed to remove excess vapors.

Envitech manufacturers a packaged vent scrubber for the control of toxic compounds like ethylene amines. Envitech's vent scrubber is simple in design, constructed out of stainless steel or other corrosion resistant materials, and available in several sizes and customizations to meet individual storage needs.

The vent scrubber uses water to capture ethylene amine vapors from any process vent.  The scrubber is designed for batch or continuous use and can meet OSHA requirements for all classes of storage tanks.  The system only requires water, power, and a drain, and installation is easy and straightforward with single point connections for all utilities.  If you are interested in more information about Envitech's vent scrubber, click on the link below to download a cut sheet for the scrubber.

Download Literature

Topics: Scrubbers, Vent

Three Things to Do Before a Stack Compliance Test

Posted by Andy Olds on Mon, Nov 02, 2015 @ 08:00 AM

Compliance testing often brings anxiety to environmental managers.  Testing is expensive and can comprise a significant fraction of the environmental operating budget.  Planning takes several months, often culminating in a tight testing window with long days and unforeseen delays.  And always looming is a dreaded phone call of a failed test.  What three things should environmental managers do to ensure a successful compliance test?

 

  1. Calibrate your control instruments

Manufacturers use complex instruments to ensure that their equipment meets its performance objectives.  These instruments must remain calibrated for the control equipment to perform properly. pH sensors, ORP probes, flow transmitters and conductivity sensors ensure optimal acid gas removal.  RTDs and thermocouples are vital to reliable operation for thermal oxidizers, condensers and reheaters.  Pressure transmitters provide important information for the performance of Venturis, and the condition of baghouse, carbon beds and packed beds.

The most common deficiency reported in our service call database is an out-of-calibration instrument.  Make sure that your instruments calibration is up to date, and check its performance a month prior to compliance testing to ensure you have the time to order a replacement instrument if required.

  1. Inspect and clean your equipment

Environmental control equipment typically faces an array of upset conditions.  Waste streams change or cycle through daily, weekly or seasonal disruptions.  Auxiliary equipment fails leading to changes in the quality of makeup water, instrument air, or power.  Repeated startups and shutdowns lead to transient states of substandard performance.  The struggle to keep environmental compliance equipment operational at all times leads to an "emergency-only" attitude towards preventive maintenance.  All of these factors lead to degradation of equipment and instruments.

Ahead of compliance testing, it is important to challenge the operations staff to inspect and clean the equipment.  Ensure instruments do not have buildup that dampens response time.  Confirm pressure drops across filters, strainers, spray nozzles are at design conditions; high pressures may be indicative of fouling.  Make sure consumables such as pH probes and filter bags are new and up to date.  Check for air ingress; most compliance tests measure the oxygen content of the gas to ensure that emissions are not artificially lowered by dilution air.  Clean sumps, separators and nozzles during regular shutdowns.  Ensure that your emissions are limited to that which occurs during steady state operation, and not from old emissions that have built up on the internal surfaces of your equipment.

  1. Interview your stack tester

The EPA has well-developed procedures for every type of emission test.  However, with ever lowering standards, stack testers are forced to push their instruments and apparatuses to their technological limit in order to accurately measure emissions.  Stack testers have found ways to extend these limits, but the difference between emissions and noise is narrowing.  Minimizing the noise, and understanding the methodology of the stack test, will ensure you and your equipment are well-prepared.

For all stack tests, ask the following:

  • What EPA procedures will you be using?
  • Are there any known interferences for the procedures?
  • What is the experience level of the stack test operators with each procedure?
  • Are you prepared for lower than expected gas flow rates, greater than expected dilution, or other flue gas variances?

For initial testing:

  • What is your expectation of the non-detectable limit with the procedure provided?
  • Is the expected non-detectable limit sufficiently low to provide accuracy below my emission limit?
  • How do you intend to reliably rig and stabilize your instruments?
  • What can I do to give the stack testers the best opportunity to provide reliable data?

If your permit has changed since your last stack compliance test:

  • Have you accounted for my new permit requirements, and how has that changed your testing protocol?

Getting ready to perform a stack compliance test?  Contact Envitech Service for a site visit to calibrate your instruments and inspect your equipment.

Contact Envitech Service

Topics: Stack Testing

Three Key Tools Envitech Uses To Improve Scrubber Service

Posted by Andy Olds on Mon, Oct 26, 2015 @ 08:00 AM

Envitech recently launched a new Service Program to provide scrubber operators with a knowledgeable and responsive resource to keep their air pollution control equipment functioning properly.  One of the service program options is true 24-7 remote plant coverage that connects operators directly with our service staff.  To be able to offer this service as a small business requires both dedication from our service team and implementation of the latest service technology.  In this post, we discuss the technologies we rely upon to offer this service. 

FaceTime

In the last year, Envitech has stepped up its use of FaceTime to remotely communicate with service technicians.  For those unfamiliar with the technology, FaceTime is an Apple application that connects users by video through their mobile phone.  Below are screen shots of a FaceTime connection using WiFi.

Envitech has found that the quality of this technology has improved such that engineers can remotely direct technicians through troubleshooting, calibration, or simple repairs.

For scrubber operators equipped with an Apple product, FaceTime provides an immediate and direct method to connect to our service technicians.  FaceTime's realtime video technology lets Envitech technicians see the issue, direct the repair, and confirm a successful outcome, all without the cost and downtime of a site visit.

GoToAssist

Envitech has invested heavily in PLC and HMI training for its engineers.  All of our engineers are capable of minor modifications of PLC logic, online changes to HMI screens, and trending data through PLC software.  Until recently, this level of assistance was not available remotely.  Older peer to peer technologies were not sufficiently reliable to allow logic interface.  HMI screens were typically built remotely and uploaded onsite by a qualified operator.  Trending was often not available "live" and had to be downloaded and transmitted by a trained software specialist.

Envitech purchased GoToAssist in 2014 to connect our engineers to our startup teams.  GoToAssist is a Citrix product that connects the user to a remote computer by invitation.  Upon acceptance of a connection, the remote engineer can manipulate the local computer.  Below is a photo of the GoToAssist software from the engineer's perspective.

Envitech has found the software to be tremendously useful, reducing our startup team sizes, shaving days off the startup schedule, and increasing the accessibility of our variety of engineering talent.  Customers have caught on, seeing how quickly and effectively we can make programming changes remotely to improve their process, and have requested this as an add-on service.  To date, we have logged over 125 support session with customers totaling more than 400 hours of remote troubleshooting using GoToAssist.

Some of the tasks our customers have enjoyed using remote troubleshooting via GoToAssist include:

  • Rescaling ranges within the logic for replacement instruments
  • Trending process and control variables to tune control loops
  • Revising HMI screens live with operator feedback
  • Downloading operational data for analysis
  • Adjusting stoking frequencies for incinerators and cleaning frequencies for WESPs

Web-Based O&M Manual

Historically, the use of O&M manuals has been the first option for maintenance and troubleshooting for the operator.  In the past ten years, component manufacturers with standard products have begun to offer their manuals via web access.  Our engineers and service technicians made use of this offering by frequently downloading a specific manual online for troubleshooting an equipment issue.

Still, most system integrators or custom manufacturers like Envitech have only delivered "binder" manuals or large PDF electronic files.  The problem with this approach is that the "binder" manuals are not very portable or sortable and often get lost or damaged.  Large PDF electronic files are often electronically misplaced and forgotten.  The result is that operators are scraping ID tags for model numbers or replacing equipment without a thought to troubleshooting or repair.

Seeing the ease of use online manuals from component manufacturers has provided, Envitech challenged itself to produce an online manual for its custom manufacturered equipment.  Starting with projects ordered in 2015, Envitech has produced an online manual for its customers.  The feedback to date has been positive, and we intend to extend this benefit to all customers via our service plan.

If you are interested in learning more about our Service Program and other features and benefits of using Envitech for your scrubber maintenance, press the buttom below.

Contact Envitech Service

Topics: Scrubber Service

Scrubber Service and Maintenance

Posted by Andy Olds on Mon, Oct 19, 2015 @ 11:00 AM

Envitech Service TeamEnvitech is proud to launch a new scrubber service and maintenance program for all users of air pollution control equipment.  Envitech offers the program to provide plant managers, environmental departments, plant engineering and operations and maintenance staffs access to our trained, experienced group of engineers and technicians.  Our goal is to improve your uptime, reduce your operating costs, ensure you meet compliance and offer you an on-demand technical resource for troubleshooting your equipment.  Additionally, we want to help you organize your maintenance programs and provide training to keep your operators up to date.

Over the past year we have strengthened our service department with technicians, tools, and training. In so doing, we have provided new and varied service to our existing customers.  For example we have:

  • Tuned a medical waste incinerator remotely to minimize CO emissions and to reduce fuel usage
  • Calibrated pH and conductivity probes prior to a successful stack test
  • Rescaled a replacement transmitter after the existing model was discontinued
  • Added HMI screens to permit trending of critical instruments
  • Upgraded VFD, PLC and HMI software to improve security of Ethernet controlled equipment
  • Precoated new cartridge filters and used Visolite to detect for filter breaches

As part of the program we offer the following services:

Our service program is built for the following equipment:

  • Quenchers
  • Packed Bed Absorbers (Scrubbers)
  • Condensers
  • Venturi Scrubbers
  • Collision Scrubbers
  • Entrainment Separators
  • Wet Electrostatic Precipitators
  • Fans
  • Cartridge Filters
  • Carbon Beds

Additionally, we maintain key relationships with other pollution control suppliers to help you service equipment such as:

  • Regenerative Thermal Oxidizers (RTO)
  • Medical Waste Incinerators
  • Hazardous Waste Incinerators
  • Afterburners
  • Thermal Oxidizers
  • Baghouses
  • Dryers
  • Cooling Towers
  • Oxidations Systems
  • Wastewater Treatment

If you are interested call or email Envitech today.

Contact Envitech Service

Topics: Scrubber Service, WESP Service

Wet Scrubber Ductwork using Rolled Alloy's 253MA

Posted by Andy Olds on Thu, Feb 28, 2013 @ 09:00 AM

Authors: Zach Schulz and Andy Olds

 

Recently, Envitech was tasked by a leading waste oil refiner in Southern California to supply and install a wet scrubber on a process gas afterburner.  The goal of the project was to reduce the sulfur emissions from the facility to avoid the SOx (sulfur oxides) reclaim program in the Southern California Air Quality Management District.  The SOx reclaim program is a cap and trade program that requires emitters to secure or purchase the right to emit sulfur into the atmosphere.  Details of the project can be found in the article "High Efficiency SO2 Scrubber Case Study for a Waste Oil Re-Refiner" which outlines the incredibly stringent SO2 emissions standards that Envitech's wet scrubber successfully met.

SO2 Scrubber resized 600

Envitech; holding a general contractor's license in California; has the capability to not only supply the wet scrubber but to also supply and install the support equipment for the project.  As the project developed, the waste oil supplier expanded Envitech's scope to include nearly all of the work required for the wet scrubber, including the supply, installation, and warranty for the ductwork from the existing afterburner to the wet scrubber system.

Envitech faced some unusual challenges with the ductwork for the existing afterburner.  The afterburner itself is composed of refractory lined carbon steel, with an average exit temperature of 1600°F and with excursions to 2000°F.  Exhaust gas from the afterburner can also contain 1000ppm sulfur dioxide (SO2) with the potential of some sulfur trioxides (SO3).  Further, 90% of the time the gas passes through a heat exchanger that reduces the temperature to as low as 600F, with outages on the heat exchanger once a week.  Thus, Envitech had to provide an exhaust duct that could handle temperatures from 600F to 2000F with an elevated concentration of sulfur compounds, cope with thermal cycling, and operate near the acid dew point.

Envitech consulted with Rolled Alloys to determine the best alloy for the design conditions.  Separately, Envitech evaluated the cost and expected lifetime of refractory lined duct.

RA 253 MA was chosen for this application for its great resistance to high temperatures up to 2000°F. It also has a very lean nickel content (11%) which is beneficial for sulfur bearing environments at high temperatures. After working with Rolled Alloys and its subcontractors, Envitech found that the cost of a refractory lined duct, including installation, was slightly higher than that of the RA 253 MA material suggested by Rolled Alloys.  Further, Envitech found that insulated RA 253 MA material would have a longer expected lifetime than the refractory lining especially due to the thermal stress created by the temperature cycling and the aggressive nature of the sulfur in the gas.

SO2 Ductwork 

With this information, Envitech presented the RA 253 MA option to the waste oil refiner and jointly agreed that the RA 253 MA material was the best option for the ductwork.  Envitech's subcontractors built the ductwork out of Rolled Alloys RA 253 MA material on-time and on-budget, with startup occurring in May, 2012.  The ductwork is still in service with no reported issues.

With the help of Rolled Alloys, Envitech was able to provide ductwork that was easy to install, cost-effective, and within budget, contributing to success on the project that has enabled the waste oil refiner to avoid the SOx reclaim program by lowering its emissions. 

The project was considered a success by all parties and Envitech is currently working with the waste oil refiner on a second wet scrubber project with similar design conditions and intends to use the RA 253 MA material.

The above article was jointly written by Zach Schultz of Rolled Alloys and Andy Olds of Envitech.  The article was co-published on the Rolled Alloys Technology blog and Envitech's Air Pollution Control Innovations blog.

Envitech is an air pollution control equipment supplier serving industrial, medical, refinery and utility customers since 1993.  Their website is www.envitechinc.com.  You can contact Andy Olds directly at aolds@envitechinc.com.

For more information on this project, please read our white paper.

Download Paper

Topics: SO2 Scrubber, Guests, Acid Gas

Seawater Scrubber Removes SO2 from Marine Diesel Engine Exhaust

Posted by Andy Olds on Thu, Apr 08, 2010 @ 03:32 PM

On March 18th, 2010 I participated on a panel discussion for the Cruise Lines International Association's Inc. (CLIA) Exhaust Gas Scrubber (EGS) Workshop in Miami, Fl. The workshop was professionally managed by BMT Designers & Planners, a navycruise ship architecture and marine engineering firm.   The panel was comprised of potential marine exhaust gas scrubber vendors.  The intent of the workshop was to provide information to cruise line participants to assess the maturity of the industry and the likelihood that exhaust gas cleaning systems will be a feasible response to the challenges of changes in regulations.

The industry is evaluating alternatives for meeting upcoming SOx emission limits under Annex VI of Marpol 73/78.  The SOx emission limits will require ships to achieve at least a SOx reduction equivalent to 0.1% sulfur fuel by 2015.  This requirement can be met by using more expensive, low sulfur fuel, or by scrubbing the exhaust gas stream.  The rules essentially require > 97% SOx removal assuming 3.5% sulfur fuel.   The International Maritime Organization (IMO) has issued Guidelines for Exhaust Gas Cleaning Systems, Annex 4, Resolution MEPC.170(57), adopted April 4th, 2008 to specify the requirements for testing, survey certification, and verification of exhaust gas cleaning (EGS) systems to ensure compliance with Annex VI.   

Envitech first started evaluating the marine scrubber application in early 2008 at the request of one of the major cruise lines.  The cruise line was interested in working with a company that could apply industrial air pollution control equipment experience to marine diesel exhaust streams on board a ship.   Envitech has deployed many particulate and acid gas scrubbers on a wide range of combustion processes including a seawater scrubber for an industrial waste incinerator at a pharmaceutical plant.  Many of these systems are similar process requirements for a diesel engine exhaust.   As a result of our evaluation Envitech developed, and recently filed a patent application for, the Hysea Marine Scrubber which is a hybrid seawater scrubber system.  We introduced this technology to the industry during the CLIA EGS workshop.

The Hysea Marine Scrubber uses available seawater alkalinity to scrub SOx.  The system is chemically assisted with caustic solution (NaOH) to achieve high SOx removal and reduced water flow rates.  The chemical consumption is minimal and estimated to be less than 7% of the usage of a closed loop, recirculation system.  The system is designed to provide flexibility to operate in two modes:

  • Open Loop/Caustic Reduced Mode - Continuous, once-though liquid discharge.
  • Closed loop/bunkering Mode - Re-circulated seawater with a small discharge stream that can be temporarily bunkered on board the ship.

The discharge liquid in both operating modes is treated to meet regulatory requirements.  Because chemical assistance with caustic substantially reduces the water flow rate, the water treatment system becomes more manageable on board a ship.  The water treatment system also re-oxygenates the water to meet chemical oxygen demand (COD) standards.

The table below shows a comparison of three different marine scrubber configurations, including:

  • Open Loop - Using once through seawater
  • Closed Loop - Using re-circulated water
  • HySea Marine Scrubber - Using chemically assisted Seawater

 

 

ITEM OPEN LOOP CLOSED LOOP HYSEA
Water
   Open Loop Mode
   Closed Loop Mode
Sea Water
Once-Through
-
Fresh Water
Re-circulated
-
Sea Water
Once-through
Re-circulated
Blowdown, gpm
    Open Loop Mode
    Closed Loop Mode

10,000
-

-
5

2,300
5
Energy Consumption, kW
    Open Loop Mode
    Closed Loop Mode

290
-

45
-

90
45
Caustic Consumption
  (est. average), gph
    Open Loop Mode
    Closed Loop Mode


0
-


-
60


4
60

A comparison of the operating parameters highlights the reduced water and power consumption of the hybrid system compared to an open loop system.  It also shows the substantial caustic reduction compared to a closed loop system.  The main advantages of the Hysea Marine scrubber include:

  • Reduced seawater flow rates - 75% - 80% Reduction
    • Reduced power consumption - 70% - 75% Reduction
    • Smaller piping - Simplified installation
    • Smaller water treatment system - Simplified installation
  • High removal efficiency -  0.1% sulfur fuel equivalent
    • Including low alkalinity seawater conditions
  • Operating flexibility to bunker a low flow discharge stream
  • Reliance on reliable and proven process technology
  • Water discharge that exceeds  discharge requirements
  • Water treated for chemical oxygen demand (COD)

Although the Hysea scrubber was designed for ship board use for a diesel engine exhaust, the same design principals also apply to acid gas scrubbing for land based industrial processes that have access to seawater.

A lot of interest in Marine exhaust gas cleaning systems was expressed during the EGS workshop. However, the cruise line industry is still evaluating the full range of options for complying with Annex VI of Marpol 73/78.  The general consensus of the panel participants is that exhaust gas cleaning is not only technically feasible, but provides a compelling financial case as a means for meeting the new regulations.

Please read our case study on reducing SO2 emissions for ships docked at ports by clicking the link below.

Download  Case Study

Photo Credit: Saint Seminole

Topics: Scrubbers, cleaning systems, Acid Gas

CFD in Air Pollution Control Systems

Posted by Andy Olds on Tue, Oct 27, 2009 @ 09:00 AM

By Mike Simon
Director of Simulation Products, Digital Dimensions

Understanding how simple design changes affect the airflow inside of Envitech's products is critical in designing efficient industrial gas cleaning systems.  Engineers who design this equipment need to analyze and understand the behavior of the components if they want to improve performance.  Computational Fluid Dynamics (CFD) is a good tool for studying the effects of different design changes on these systems.  CFD provides a way to save time and money in obtaining the necessary information, and assists engineers in designing better quality air pollution control systems.    The use of CFD makes it possible to minimize the use of physical prototypes and find serious flaws much earlier in the design process. 

SolidWorks is the 3D CAD system used by Envitech to design their industrial gas cleaning systems.  SolidWorks has a number of complementary features to its mechanical CAD system including CFD capabilities that are fully integrated within the main CAD interface.  SolidWorks Flow Simulation is the name of the CFD program inside of SolidWorks that allows engineers to take their 3D CAD models and perform virtual prototyping on their designs without having to fabricate any parts.  To perform a simulation, the following steps are needed:

  • 1. Create solid model in the SolidWorks CAD system
  • 2. Specify the working fluid ( air was used in this case)
  • 3. Specify the flow rate at the duct inlet
  • 4. Specify the outlet opening of the duct
  • 5. Specify the pressure drop or resistance properties of the filter material (properties taken from filter manufacturer specifications)
  • 6. Run the simulation inside of the SolidWorks interface

Flow Simulation

 

Envitech's products were particularly challenging since Envitech's products utilized very thin fins and packing materials within a large ducting area.  Thin fins are used to direct the airflow and also to collect water from entering the system.  SolidWorks Flow Simulation was able to capture the geometry of these thin fins and create a corresponding CFD model for the simulations.  Packing material is used to help distribute airflow and trap particulates from being released into the environment.  The porous media feature inside of SolidWorks Flow Simulation was used to simulate the packing material and create the additional resistance to the airflow.  After performing the simulations, the Envitech engineers had the ability see the effectiveness of the scrubber fins in directing the airflow and to understand the pressure drops caused by the packing material.  The simulations helped the Envitech engineers validate their designs and gave them additional insight into how to improve future product performance.

For additional information on SolidWorks CAD or SolidWorks Flow Simulation software, go to http://www.ddicad.com/ or contact Mike Simon, Director of Simulation Products, at msimon@ddicad.com.

For a case study on the impact of CFD analysis, click on the link below.

Download  Case Study

Topics: Venturi scrubbers, Scrubbers, wet electrostatic precipitators, Guests

Guest Blog: CFD Analysis

Posted by Andy Olds on Mon, Oct 26, 2009 @ 01:48 PM

Digital DimensionsI am very excited to announce that we will be publishing our first special guest blog post tomorrow, Tuesday, October 27.  The topic of the blog will be CFD analysis in air pollution control systems.

Our guest blog author is Mike Simon, Director of Simulation Products at Digital Dimensions.  Mike is a former SolidWorks/Cosmos Technical Manager and he has 10 years of FEA/CFD experience at companies such as General Atomics and General Dynamics.  Mike earned a BSME from UCSD, a MSME from Stanford, and a MBA from USD.  I am sure you will find his article very interesting.

A little more background Digital Dimensions...In addition to being an authorized reseller of Solidworks, Digital Dimensions hosts a variety of Solidworks training sessions, including topics such as structural analysis, flow simulation, and heat transfer - all tools available in the Solidworks design package.  I personally have benefited tremendously from the training sessions, and would recommend it to anyone interested in CFD or structural analysis using 3D models.  I use the CFD analysis on many of our Venturi scrubber designs as well as for our wet electrostatic precipitators.

Topics: Guests

Pharmaceutical Scrubber

Posted by Andy Olds on Tue, Oct 13, 2009 @ 04:50 PM

pharmaceutical scrubberAs the EPA continues to tighten the emissions belt, I am seeing new industries with air emissions issues. One such industry is pharmaceuticals, who are now more commonly regulated for acid gases on post-combustion devices.

Pharmaceutical air emissions are typically a result of an organic fume from a solvent. The fume, containing vaporized solvent, is captured either within a fume hood or central ventilation system. When regulated, the most effective way of removing a fume is to combust it in a regenerative thermal oxidizer (RTO) or some other combustion device.

The combustion of a solvent such as methyl chloride in an RTO leaves three compounds: carbon dioxide, water vapor, and hydrochloric acid. The last of the three - hydrochloric acid - is often treated as an emission and if so must be removed from the outlet exhaust.

Pharmaceutical Scrubber 

The most best method for removing hydrochloric acid from a gas is the use of a pharmaceutical scrubber. A scrubber offers extremely high efficiencies (greater than 99%, or as required) at a low pressure drop. Recirculating neutralized water across a packed tower, the capital and operating cost of a scrubber is minimal. Further, the effluent from a HCl scrubber contains only sodium chloride - table salt - and can easily be disposed of through a wastewater sewer with little to no further treatment. Using FRP for the scrubber provides a low cost building material highly resistant to acid attack.

Hydrochloric Acid Corrosion

The removal of hydrochloric acid from a combustion exhaust does offer one particular difficulty over other common acid gases, of which designers and operators in the pharmaceutical industry need to be wary. Hydrochloric acid and neutralized chlorides are very aggressive towards most metals, especially so at elevated temperatures typically seen on the outlet of a combustion process. Since the HCl is contained in the exhaust of a combustion process, the inlet gas temperature to the scrubber is high. In turn, the recirculation water temperature is also high, usually well above 100F. Standard metallic materials such as stainless steel will quickly corrode in this environment.

In the past, I have used both AL6XN and hastelloy for metallic materials in HCl scrubber systems. Common metallic items in a pharmaceutical scrubber include the quencher, instrumentation, and downstream devices.  AL6XN is a duplex material that provides very good corrosion resistance to around 1000F. It also has about an order of magnitude greater chloride pitting resistance than stainless steel at neutral pH, and over two magnitudes resistance at low pH.  AL6XN is ideal for quenchers on the exhaust of an RTO, where the outlet temperature is usually around 500F. Hastelloy is more expensive, but it offers heat resistance to 2500F as well as a further order of magnitude resistance to chlorides over AL6XN.

Hydrochloric Acid Mist

The other issue provided by hydrochloric acid in a gas stream is the formation of hydrochloric acid mist, which I have previously touched upon in my acid gas dewpoint post.

Hydrochloric acid mist usually requires a high efficiency mesh pad for removal of any HCl aerosols that may form in the scrubber.  A mesh pad is more expensive than a standard wave form mist eliminator, and is also much more prone to particulate plugging.  If hydrochloric acid is in your gas stream, make sure you consider a mesh pad and beware of particulate!

If you would like to learn more about corrosive acid gas scrubbers, download the free case study below.

Download  Case Study

 

Topics: Scrubbers, Acid Gas, quenchers