High Energy Jet Venturi Fume Scrubbers
In 1917 Croll Reynolds began manufacturing vacuum steam ejectors. Starting in the 1950’s this jet venturi design was adapted for use in pollution control. With the passage of the clean air act in the 1970’s, CR developed a high-energy design which could efficiently remove particulate matter.
CR Clean Air’s high energy venturis are so termed because they use the energy from a high velocity gas stream to atomize a liquid stream. The venturis spray nozzles, oriented perpendicular to the gas flow, are specially designed for maximum performance. The high atomization of the liquid and the extreme turbulence in the venturi throat entrain the solid particulate in the liquid phase, resulting in a unit with low utility consumption and maximum performance, and give this scrubber its exceptionally high ability to remove both micron and sub-micron dust particles. These nozzles can handle a wide range of situations, including slurries and can be easily removed and replaced when needed.
Our high energy scrubbers are available with a fixed throat design for specific gas flow, or an optional variable throat design which can be adjusted to fluctuating operating conditions. In most applications, a fixed throat venturi is preferable because of its lower initial cost and reduced maintenance due the lack of moving parts.
Variable throat designs, which can be either manual or automated, are typically only utilized for situations where high turndown is required. Our process engineering experts can guide you as to which design will be best suited to meet your requirement.
The gas from the venturi section is normally discharged into a cyclonic separator tank. A spin is imparted as the gas enters the separator so that the liquid is driven to the outside wall via the rotational motion of the gas. The liquid is then collected and returned to the sump where it can be recycled.
At the top of the separator tank, a mist eliminator, typically a Chevron blade type, is ·used to ensure minimal liquid entrainment in the effluent gas, and thus the highest removal efficiency possible. This separator / mist eliminator design is particularly well suited to variable gas flows since it is effective over a wide range of operating conditions.
CR Clean Air custom engineers all of its products to ensure that the equipment is optimized for your plant’s needs. We can provide the jets in either a vertical or horizontal orientation depending on the space available at your location. Our rigorous quality and attention to detail help set us apart. If it has to work, the first time and every time, you can trust CR Clean Air High Energy Jet Venturis.
Performance: For maximum efficiency, it is important that the venturi and corresponding tank be carefully sized for the specific application. Here are some of the reasons it is important to let our specialists help you select the High Energy Scrubber you need:
1 – Particulate Loading – There is a ‘sweet spot” where a high energy venturi will work the best. Too much particulate, and the unit becomes overwhelmed.
Too few particles, and the odds of them “slipping through” particularly with smaller particulate. The ideal particulate loading is a function of both jet size and particle size, but historically 0.4 gr/ft3 (915 mg/m3) of gas flow is optimal for most applications.
2 – Particle Size Distribution – The smaller the particle, the harder it is to entrain. If you have a particle distribution summary, that will help us ensure that from the largest particles to the smallest, the design is optimized as much as possible. All of our venturis will capture 99% of particles larger than 10 micron excepting very heavy particulate loadings. For 10 to 1 micron the amount of capture is 99% except for very lower pressure drop units. For the specific removal in the sub-micron range, our application specialists can apply their property models to determine the exact removal you can expect.
3 – Fixed vs. Variable Throat – For applications where variation in gas flow rate requires throat velocity compensation in order to maintain a specified scrubbing efficiency, CR Clean Air offers variable throat designs.
For small to moderate changes in flow, variable throats are not necessary.
Even when operating ± 20% from the design condition, overall removal rates can be held for a given particle size. This is true because at higher liquid to gas ratios the efficiency increases for a given velocity through the throat. The slightly lower velocity through the throat is compensated by the slightly higher liquid to gas ratio so that the net effect is no difference in performance.
Where higher variations are anticipated, a variable throat is essential. Available with either automatic or manual control, the automatic throat is used where flow conditions vary widely and frequent adjustments are required. For situations where only occasional variations occur, such as during an upset condition, the manually controlled throat is generally sufficient.
3 – Once-through vs. Recirculating – Although the majority of our systems recirculate the scrubbing liquid, for small liquid flow rates or high particulate loadings, it often is more beneficial to use a non-recirculating (“once-though”) system. Thankfully, because the nozzles are specifically designed to prevent plugging, high concentrations of solids (up to 20 wt%) can be handled without difficulty – making the once through system less common than they once were.
4 – Systems Components – A CR Clean Air High Energy scrubber is available as individual unit (jet only) for incorporation in your own design or as a complete package systems, including recirculation pumps vales, instruments and controls. From the basic to the complex, we will be there every step of the way to assist you in designing a customized solution to meet your process objectives.
Ease of maintenance: Excepting the variable throat design, the CR Clean Air High Energy Scrubber has no moving parts thus maintenance is minimal. It is recommended that the unit is inspected during normal plant shutdowns. Particular attention should be paid to the spray nozzle, which will wear over time and in some cases, may become clogged. Additionally, the body should also be checked for signs erosion particularly the throat section where the highest velocity occurs. The corresponding separator tank rarely needs maintenance, although the mist eliminator should be given a visual inspection periodically.
It is always advisable to have a spare spray nozzle on hand, since these are custom designed and not a stock item. Most of our clients also keep a spare set of gaskets on hand, and some go as far as to have a spare mist eliminator for the separator tank. Thankfully most of our installations go years, sometimes decades, without any need for service or replacement parts.
Materials of construction: Given the severe conditions our equipment is typically placed under, material selection is of primary importance. We fabricate out of a wide range of materials, both metallic and non-metallic. From fiberglass reinforced plastics (FRP) to exotic alloys and everything in between we have the capability to supply what you require.
For most low temperature service, FRP is common. We can also fabricate in CPVC, PVDF, polypropylene, HPDE and even offer dual laminates. Metallic options include Carbon steel, stainless steel, duplex stainless, as well Incoloy or Hasteloy alloys. Other alloys are available should your application require it. Additionally, we can offer units with a suitable lining such as rubber or Teflon when necessary.
We work with our clients to identify the material that will offer an appropriate blend of service life vs. initial cost. Given that transient process parameters, from a spike in temperature during an upset, to an otherwise minor component in the gas flow may alter the resistance of materials to attack, your own experience with other equipment in similar service, or the upstream material is often the best guide. When this previous experience is not available we can draw on our extensive case history file to determine what will, and more importantly will not, stand the test of time.