Envitech recently got noticed in a local news story by Michael Chen of Channel 10 News, “Local Company Helps Dispose of Ebola-tainted Waste”. The story talks about the challenges of processing Ebola waste and how Envitech’s Medical Waste Incinerator Scrubber at the University of Texas Medical Branch (UTMB) was used to dispose of waste generated by an Ebola patient in Texas.
UTMB operates the only permitted medical waste incinerator in the state of Texas. Since 1991 the facility has operated an incinerator which uses an Envitech wet scrubber system to clean the exhaust gases of harmful pollutants. A new incinerator system was recently installed to meet the new EPA rules promulgated for the hospital, medical, and infectious waste incinerator (HMIWI) maximum achievable control technology (MACT) standard. The impact of these rules is discussed in a previous blog post.
The outlet emission requirements of the new standards are a significant reduction from the previous 1997 standards. The allowable outlet emissions for many of the metals, i.e. lead (Pd), Cadmium (Cd) are less than 1% of the previous emission limits. For example, the allowable concentrations for Pb,and Cd are measured in 10-7 and 10-8 gr/dscf, respectively. These are some of the lowest HAPs emission limits for industrial sources in the United States. Below is a summary performance guarantee for the new scrubber system based on the new HMIWI standard:
- PM < 18.3 mg/dscm (0.008 gr/dscf)
- Lead < 0.00069 mg/dscm (3.0 x 10-7 gr/dscf)
- Cd < 0.00013 mg/dscm (5.7 x 10-8 gr/dscf)
- HCl < 5.1 ppmv dry
- SO2 < 8.1 ppmv dry
- Dioxins/Furans < 0.035 ng/dscm on TEQ basis
Recent episodes of processing highly infectious waste from Ebola patients may re-ignite a policy debate on medical waste disposal. In the early 1990, many hospitals were going to a model of owning and operating a relatively small medical waste incinerator to process and destroy medical waste generated in-house. These systems typically have a capacity of 500 to 1,500 lb/hr. As air emission standards became stricter, many hospitals decided to shut down their incinerators and ship their waste to larger, centralized medical waste incinerators. These systems are much larger in capacity. For example, the largest medical waste incinerator facility is in Baltimore, MD with a permitted capacity of 150 ton/hr. The trade-off of a centralized waste incinerator is the risk and liability of transporting the waste on public roads and highways. The recent Ebola outbreaks bring to light that some of this waste can be highly infectious and pose a significantly greater risk to public health. It also came to light that a single Ebola patient generates a substantial amount of infectious waste. In this scenario, it may make more sense for facilities to have the capacity to destroy their own waste and avoid the risk of transporting it over great distances on public roads.
The advancement of scrubber technology and compliance with the new, more stringent EPA MACT standards, confirm the ability to operate medical waste incinerators with virtually no harmful emissions into the air. In addition to the UTMB medical waste scrubber system, Envitech has upgraded several other medical waste incinerators for meeting the new standards. Based on the extreme low emission limits, the results are truly groundbreaking and may encourage states and facilities to permit new systems.
In 2012 Envitech designed and built a marine diesel scrubber to remove SO2 from the engine exhaust of ocean going vessels. The scrubber was integrated into the Advanced Maritime Emissions Control System (AMECS) used at the Port of Long Beach. AMECS is a stationary system that uses a bonnet to capture the exhaust gas from the ships stack while at port. The exhaust gases are conveyed to AMECS to clean the gases of particulate (PM), NOx and SOx before exhausting to atmosphere. This allows the ship to operate its auxiliary engines and boiler system while at port to provide power to the ship. AMECS provides a cost effective way for ships and port operators to reduce emissions and to meet tougher regulatory standards.
The AMECS team recently announced that the California Air Resource Board (CARB) has approved AMECS as an alternative technology for the At-Berth Regulation. This approval follows more than 1500 hours of validation testing on 40+ vessels during 2012 and 2013. The most recent testing occurred in October of 2013 and was attended by representative of CARB and SCAQMD as well as representatives from the Ports of Long Beach and Los Angeles. The test yielded impressive results, including:
- NOx (@1.6ppm ammonia slip) 99+%
In a parallel track, the maritime industry is looking for ways to meet tougher standards not only at port but while operating at sea based on the IMO Annex VI MARIPOL Tier III requirements. Envitech continues to develop De-SOx technology options for ship based marine diesel engines. The recent CARB approval is a milestone achievement for demonstrating the Envitech scrubbers ability to achieve high SO2 removal efficiency over a wide range of diesel exhaust and operating conditions.
Click on the link below to download a case study on the marine scrubber.
With an expanding global population, demand for minerals continues to grow. Development of non-traditional resources is expected to increase to meet this growing demand. This includes copper resources challenged by high levels of arsenic. Mining operations may incur penalties for arsenic in concentrates that exceed a certain amount. As ore with low levels of arsenic is depleted, these penalties will continue to rise.
One facility seeking to reduce the impact of penalties is the Aranzazu project in Zacatecas Mexico by Aura Minerals. The facility will use a partial roasting technology by Technip to achieve arsenic reduction in the concentrate. After treatment, the concentrate is expected to contain less than 0.3% arsenic. This will decrease expected arsenic related penalties by up to $1.00 per payable pound of copper produced.
The roaster off-gas will be treated by an Envitech wet scrubber system to remove arsenic with a 99.9% performance guarantee. The inlet gas to the scrubber will be at an elevated temperature well above 1,000oF and will have a high concentration of particulate, sulfur, and arsenic. The scrubber system combines Envitech’s wet scrubber technology which has been used to remove hazardous air pollutants from medical and hazardous waste incinerators with Envitech’s wet electrostatic precipitator technology (WESP) for final collection and removal of arsenic. Envitech’s WESP technology has demonstrated high performance for arsenic removal on other furnace applications at secondary lead smelting facilities.
A geothermal plant produces a sustainable source of energy by converting super heated fluids from the earth’s geothermal resources into electrical energy. The fluids are recovered in the
process and re-injected back into the earth. The following YouTube video from CalEnergy provides a good overview of how a typical geothermal plant works. California currently obtains about 4.5% of its electricity from geothermal plants. Most of these plants are sized at 50 MW but some plants can be larger in the 150MW range. There is an estimated 2,300 megawatts of undeveloped energy in an area in Imperial County California near the Salton Sea just outside of San Diego.
The geothermal energy conversion process generates a sulfur containing off-gas which passes through a thermal oxidizer to destroy volatile organic compounds (VOC’s). The sulfur compounds are oxidized to sulfur dioxide (SO2) and must be removed before exhausting to atmosphere. A packed bed absorber treats the thermal oxidizer exhaust to remove SO2. Often times geothermal plants are located in an extreme desert environment with summer temperatures reaching > 120oF. The scrubber equipment must be designed to achieve high removal efficiency, continuous operation and withstand the extreme environment.
Click the link below to download a case study for an SO2 scrubber installed at an ORMAT geothermal plant near the Salton Sea in Southern California.
A previous blog post made a case study available for wet electrostatic precipitator (WESP), SO2 scrubber system that will treat the off-gas of a red liquor recovery boiler for a sulfite pulp mill in Quebec, Canada. The scrubber system is part of a larger green energy project that will produce 40-megawatts of power and increase annual production capacity of specialty cellulose by 5,000 metric tonnes. The new production capacity is slated to be complete by September 2014.
The system is comprised of a sulfur recovery island that cools the boiler exhaust gases and recovers sulfur using ammonia as a scrubbing reagent. The sulfur containing effluent is re-used in the cellulose producton process. The sulfur recovery island is followed by a gas cleaning island comprised of an packed bed SO2 scrubber integrated with an Envitech wet electrostatic precipitator (WESP). The gas cleaning island removes SO2 and particulate before exhausting to the atmosphere.
Envitech has completed the system design and released major equipment orders. Some major components will be complete as early as this month. Delivery will take place before the end of 2013. The adjacent and above images show a recent rendering of the system.
Envitech recently got noticed in a local news story by Michael Chen of KGTV Channel 10 News, “San Diego Companies Could Help Clean China’s Air”. The story is about how California’s Governor Jerry Brown’s diplomatic trip to China could lead to opportunities for local San Diego companies like Envitech. During his visit, Gov. Brown signed a pact that will pave the way for California companies to help China measure and improve its air quality. As a leader in industrial air pollution control equipment, Envitech has process technology that can be used in China for reducing hazardous air pollutants (HAPs) and pollutants that contribute to regional haze like sulfur dioxide (SO2). These technologies have been applied to many processes in North America including a coal gasification plant, hazardous waste incinerators, lead smelters, sulfite pulping mills, waste oil re-refiners, geothermal plants, and mining and mineral processing to name a few. Envitech has pursued several opportunities in China through 3rd party customers and will have one installation starting up later this year.
In 2009 I wrote a blog piece about the new EPA rules promulgated for the hospital, medical, and infectious waste incinerator (HMIWI) maximum achievable control technology (MACT) standard. The compliance dates for these rules are fast approaching. Facilities with existing equipment must demonstrate compliance to the new standards by October 2014. Envitech is already under contract with several facilities to retro-fit existing medical waste incinerator scrubbers with add-on control equipment to meet the new standards.
The emissions reduction challenge with the new rules can be seen in the adjacent graph which compares the difference between the 2007 MACT standard to the new MACT standard. Stack emissions must meet substantially lower limits for Cd, Pb, and Hg. In many cases, this requires add-on controls capable of greater than 90% removal of sub-micron condensed metals. Most facilities are putting on a re-heat and filter package to remove the condensed metals. A few will use wet electrostatic precipitators (WESP) which are more expensive. The ability to meet the new rules using a re-heat and filter package has been demonstrated for lead and cadmium on a commercial and industrial waste incinerator (CISWI). The WESP capability has been demonstrated for reduction of lead emission achieved at a secondary lead smelter in California.
Another emissions reductions challenge is dioxins/furans (D/F). Emission limits for D/F have been reduced from 125 ng/dscm Total and 2.3 ng/dscm TEQ (corrected to 7% O2) to 25 and 0.6 ng/dscm, respectively. These emission limits are too low to be met with carbon injection. An add-on control package of re-heat and carbon bed absorber is required to meet the new limits.
Solutions to these challenges exist and facilities are taking steps to meet them. Click on the link below to download the HMIWI MACT Rule paper from the 2010 International Conference of Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC).
Venturi scrubbers are used to remove particulate from the exhaust gas of industrial sources. They are highly efficient at removing particulate 1-micron in size and larger. Venturi scrubbers are used in solid waste incineration, waste-to-energy production, mining, biosolids sludge processing, plastics production and coal gasification. In many of these applications, the Venturi is used on the back end of a dryer or thermal destruction device.
In accordance with Bernoulli's equation, inlet gas accelerates at the converging section, increasing gas-liquid contact. As water is injected perpendicular to the gas flow, the accelerated gas particles are captured by water droplets upon collision. The resulting droplets aggregate through the diverging section and are separated from the process gas by the mist eliminator (ME) in the entrainment separator (ES).
The ability of the mist eliminator to remove water droplets from the gas stream can have a significant impact on the scrubber performance. Any water droplets that "escape" the ME will carry entrained particulate which can foul a stack test and increase the measured outlet emissions. The amount of pressure drop consumed by the ME can impact scrubber performance. Minimizing ME pressure drop allows a higher pressure drop across the Venturi which increases the particulate capture efficiency in the Venturi throat.
The mist eliminator efficiency is heavily impacted by velocity. Therefore, it is critical to achieve even flow distribution before reaching the ME. The ability to distribute the flow uniformly will allow the system to operate more effectively under a wider range of inlet gas flow rates.
Flow studies were performed to evaluate the capability of three different designs:
- Envitech design
- Design from an ES supplier (referred to as Config. 1)
- Design from a customer based on past experience (referred to as Config. 2).
All three systems have their respective "plate" design to help improve the flow distribution.
Differential pressure (∆P) across the mist eliminator is a direct indicator of how well distributed the flow is; the lower the ∆P, the more evenly the flow is distributed. The graph below compares the ∆P across the mist eliminator and the plate respectively for the three designs. The ideal ∆P across ME was obtained at uniform inlet gas flow through the ES. Envitech's design has the lowest ∆Ps, reflecting that the plate distributes the flow most effectively and as a result the ∆P across ME is the closest to ideal.
To provide a visual illustration, the cut plots below were obtained from flow studies showing the velocity(y) distribution prior to the plate, before and after mist eliminator. A zone with high velocity (red) was observed in all designs before entering the plate. The plate breaks up the hot spot and re-distributes the flow. The flow pattern before and after the ME for the Envitech design is the most homogenous among the three which is consistent with the pressure drop results.
The flow studies enabled the Envitech Venturi Scrubber to be optimized three ways as follows:
- Reduced the material cost wiwthout compromising scrubber ability to agglomerate and remove particles.
- Refined the flow distribution to expand the process window in the entrainment separator.
- Reduced the pressure drop across the ES which allows a higher pressure drop across the Venturi throat.
The purpose of a wet electrostatic precipitator (WESP) is to remove particulates that are smaller than one micron from a gas stream. One of the common industrial applications is downstream of standard pollution control equipment on power plants or pulp mill facilities. Power plants typically use wet electrostatic precipitators after all other pollution control equipment for polishing. Pellet mill facilities use wet electrostatic precipitators upstream of RTOs to prevent buildup on the RTO media. Particulate removal is achieved by sending process gas through an array of high voltage electrodes and grounded collectors. Particles in the gas are charged and then attracted to the collector surface; clean gas continues up the WESP.
The outlet section of a WESP houses the insulator compartments. Insulator compartments support a high voltage grid which holds the discharge electrodes in place. This arrangement separates the high voltage grid from the grounded section. The introduction of purge air through the insulator compartment reduces dust and moisture buildup on the walls of the compartments. This not only keeps the insulator bushing clean but also maintains a positive air pressure to prevent process gases from entering the compartment.
The diagram above shows how the WESP is connected to the insultator compartment with a shroud. Operating the system at minimum purge air flow helps reduce operating cost as less energy will be required to heat up the purge air. The caveat here is that inadequate flow will result in wet process gases swirling into the insulator compartment through the shroud from the WESP. In an attempt to optimize our operating conditions, flow simulation was performed to analyze the flow pattern of purge air through the shroud at varying inlet flow rates.
The close-up view of the shroud shown on the bottom was taken facing the insulator compartment with WESP at the back. The green/blue color indicates air flow towards the WESP (into the page), while the red/yellow represents flow towards the insulator (out of the page). This illustrates a positive air flow into the WESP achieved at minimal flow rate. Under this operating condition, energy savings will be maximized while ensuring no swirling of wet process gas into the insulator compartment.
Envitech will be attending the International Biomass Conference & Expo in Minneapolis, MN April 8-10, 2013. We will exhibit at Booth 807. During the conference I will be presenting in the Pellets & Densified Biomass track between 8:30 am and 10:00 on Wednesday, April 10th. The topic will be "High Performance Wet Electrostatic Precipitator (WESP) for Pellet Mills".
A large portion of wood pellets produced in North America are exported to Europe to support aggressive low-carbon fuel incentives. Growth of the export market has lead to
large scale pellet mills with production capacities ranging from 500,000 to 750,000 tons of pellets per year.
These mills use wood dryers to remove moisture from incoming feed material. A wet electrostatic precipitator (WESP) collects particulate (PM) and condensed volatile organic compounds (VOC) from the dryer exhaust. This is required to protect a downstream regenerative thermal oxidizer (RTO) from fouling. The RTO destroys volatile organic compounds (VOCs) before exhausting to the atmosphere. The process flow conditions are large and typically several hundred thousand cubic feet per minute.
This presentation will discuss a high performance WESP design to treat the pellet mill dryer exhaust. The design leverages experience from several large flow rate applications including a coal dryer scrubber, secondary lead smelter WESP, and sulfite pulp mill recovery boiler WESP. The presentation will focus on how the design achieves high performance.