Combining Tech Helps with AC Transloading

Automated scraper strainers paired with macerators eliminate high volumes of large, suspended solids from slurries for a “set it and forget it” approach. All photos courtesy of Acme Engineering

Automated scraper strainers paired with macerators eliminate high volumes of large, suspended solids from slurries

In the asphalt industry, industrial strainers are used to separate unwanted suspended solids from liquids and slurries for efficient transloading, in which asphalt is heated to a liquid form and transferred from tank cars to trucks or from trucks to tank cars at rail facilities. However, conventional strainer methods can be improved upon to keep debris or solids of substantial size or quantity out of the liquid.

A novel blend of industrial wastewater technologies now allows for the efficient removal of solids without the need for extensive manual labor and so on. Specifically, the design involves the combination of a macerator, which breaks down large solids into smaller fragments, and an automated scraper strainer flexible enough to filter out larger debris along with tiny particles. This innovative solution is even designed to accommodate high solids loading without clogging.

The combination of these two established technologies is already being applied to some of the toughest straining applications including asphalt transloading, wastewater debris, power plant boiler water slag and meat processing waste streams. Our interest here is asphalt transloading.

“Although the macerator cuts up the biggest solids, the strainer must still be able to separate both relatively large pieces and tiny particles while handling high solids loading without becoming obstructed.”—Robert Presser

Overcoming Traditional Limitations

Duplex strainers are often used in continuous flow processes that cannot be shut down for cleaning purposes. Duplex basket strainers employ two distinct chambers that function independently. When one chamber needs cleaning, the flow is diverted to the alternate chamber, enabling the removal and cleaning of the first basket.

Cleaning is a laborious process that involves equalizing pressure between the baskets, diverting flow to the off-line chamber, opening the cover, manually removing the clogged basket, and cleaning it before refitting the basket, ensuring the seal and tightening the fasteners.

An automated scraper strainer like that from Acme Engineering is designed to continually remove both large and small suspended solids from liquids and slurries.

If an operator fails to adequately clean the basket strainers for any reason, both strainers can become clogged at the same time. This compromises the filtration process, resulting in quality issues or unexpected downtime until the problem is resolved. For many processors, this can occur simply due to having insufficient personnel to keep basket strainers clean along with their other duties.

“As an alternative, a combination of established complimentary technologies such as a macerator and an automated scraper strainer can essentially ‘knock out’ even the toughest problems related to large solids and high solids loading in an automated way,” said Robert Presser, vice president of Acme Engineering Prod. Inc., a North American manufacturer of industrial self-cleaning strainers. The company is an ISO 9001:2015 certified manufacturer of environmental controls and systems with integrated mechanical, electrical and electronic capabilities.

In this configuration, a macerator would be installed upstream to reduce large solids down to a manageable size. The capabilities of the automated strainer are crucial to the process as well, according to Presser.

“Although the macerator cuts up the biggest solids, the strainer must still be able to separate both relatively large pieces and tiny particles while handling high solids loading without becoming obstructed,” Presser explained.

Adapting strainers for the specialized filtration of uncommon liquids and slurries requires not only expertise but also collaboration with the processor as well as some design iterations.

In the case of Acme, the OEM’s automated scraper strainer is designed to continually remove both very large and very small, suspended solids from liquids and slurries. Cleaning is accomplished by a spring-loaded blade and brush system, managed by a fully automatic control system.

Four scraper brushes rotate at 8 revolutions per minute (RPM), resulting in a cleaning rate of 32 strokes per minute. The scraper brushes get into wedge-wire slots and dislodge resistant particulates and solids. This approach enables the scraper strainers to resist clogging and fouling when faced with large solids and high solids concentration.

Blowdown typically occurs only at the end of the intermittent scraping cycle when a valve is opened for a few seconds to remove solids from the collector area. Liquid loss is well below 1% of total flow.

If additional pressure is required to clean the screen, Acme Engineering can add an inexpensive trash pump to the blowdown line to assist in removing the solids from the strainer sump.

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“Since the solids are small, a little trash pump can pressurize the blowdown line to evacuate solids from the strainer. The combination provides quick ROI because operators no longer have to monitor and clean out heavily loaded basket strainers, resulting in substantially less labor and downtime,” Presser said.

Alternatively, the sump can be replaced by a cylinder bracketed by two gate valves that open and close as needed to remove the solids waste.

“When you are ready to empty the cylinder, you close the top gate valve momentarily and open the bottom one by depressing a button to dump the accumulated solids into a receptacle like a dump truck or a conveyor bucket so there is no manual handling required,” Presser said.

According to Presser, Acme has worked with operators and managers at rail facility intermodal terminals to implement a wide range of specialized straining systems for difficult applications with exceptionally large solids or very high solids loading.

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In one example, the OEM installed equipment to strain asphalt slurries at intermodal terminals providing rail-to-truck and truck-to-rail transloading services. One application involved using multiple cylinders with gate valves to appropriately strain liquid asphalt to the correct specification for rail-to-truck loading.

According to Presser, adapting strainers for the specialized filtration of uncommon liquids and slurries requires expertise and collaboration with the processor and some design iterations.

“For unusual applications, it may take a few attempts to get it right. You may have to adjust the timing and frequency of cleaning as well as adjust the screen slot size. There are quite a few variables involved,” Presser concluded.

For more info, visit Acme Engineering Prod. Inc. at acmeprod.com.

Solve Asphalt Plant Odor Issues

Editor’s Note: For 2024, AsphaltPro Magazine allows experts in the industry to share how to expand your operations to the next phase of business. Are you ready to start making your own hot-mix asphalt? Let’s turn to some professionals who have equipment, services, software and tenure to help you expand to mix design, production, hauling and more. This month’s installment from Ecosorb takes a look at the permit line-item of odor control at the plant to ensure your community relations, sustainability initiatives and production efficiency are working hand-in-hand.

In the asphalt industry, maintaining neighborly relations and curtailing odor complaints before they arise is just as important as maximizing production for every company’s long-term business continuity.

Asphalt binders are complex mixtures of organic compounds produced as a byproduct of petroleum refining. With constantly changing feedstocks, staying on top of blends is critical to controlling odors. In recent years, “opportunity crudes” have become more prevalent industrywide, and it has become necessary to balance the lower cost of these crudes with extra processing and off-gas scrubbing requirements. Another factor to consider is increased equipment maintenance and premature failure because of accelerated corrosion caused by hydrogen sulfide in lower grade crudes.

Each peak in a GC chromatogram represents the presence of a compound, identified and quantified on the x- and y-axes respectively.

During heating, mixing, transfer and application of asphalt binders, odors are often produced from volatile organic compound (VOC) emissions, which can lead to concerns from neighbors and passersby smelling the off-gas. If left unaddressed, concerns can become complaints, which can ultimately pave the way to regulation and operational restrictions.

Odor abatement is a historically difficult undertaking in the asphalt industry because of the complex makeup of bindings and numerous petrol products used in each hot mix. However, plants can now enlist the help of top suppliers with the knowledge and advanced laboratory technologies needed to chemically neutralize odor-causing components. These experts address this issue by identifying the problematic compounds, and by then creating and providing additives specially formulated to neutralize odors from various asphalt mixes.

Neutralization challenges with evolving mixes

Occupying a lower tier on the crude refining food chain, asphalt blends will always vary much more than higher-tier products, such as aviation fuels. Mixes can vary significantly from one season to the next—particularly with opportunity crudes—depending on the oil sources available and how they are processed. As a result, odor neutralization formulations must also adapt to the changing constituents of each season’s asphalt mixes.

Manufacturers, therefore, cannot always rely on the same odor-mitigating additives from one season to the next, even when producing the same end product. Additionally, since crude sources and refining processes vary by region and supplier, the nature and intensity of odors can differ even between batches of asphalt binders. Other factors for odor mitigation assessment include the temperature at which the plant is operated, geographical attributes—such as hills and valleys—humidity, temperature, wind speed and direction, and proximity of neighbors.

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There are many potential VOC emission sources during the processes of refining the feedstock, manufacturing the mix, and storing the finished product. This is especially notable during the storage of bulk asphalt in a heated tank, in addition to stack emissions during production. Loading asphalt from one vessel to another—such as from the silos into trucks, and from trucks into a paver hopper—is another frequent odorous phase.

VOC concentrations increase significantly at higher temperatures. Below 150°C, few detectable VOCs are produced, but above this point, emissions increase. VOC prevalence is also dependent on the surface area of asphalt exposed to air over asphalt-coated aggregates. VOCs also increase substantially when these asphalt-coated aggregates are agitated.

Ecosorb’s vapor phase delivery system is useful for mitigating odors in airborne particulate matter at a baghouse.

Research-driven and plant-based solutions

Asphalt production variability spawns the need for adaptive and sometimes customized blends. Although there is no one-size-fits-all solution, there are general formulations that bolster odor mitigation efforts for a variety of asphalt mixes. These general formulations are added to the mixes to neutralize several odor-causing constituents, like hydrogen sulfide, mercaptans and general hydrocarbons. Specialty suppliers update their additives from year to year based on aggregate samples taken at asphalt plants to maintain effectiveness.

Although general formulations are efficacious for many mixes, some plants require custom blends, and expert suppliers can help with these needs as well. In these situations, asphalt samples are taken from the plant during multiple stages of production. These samples are then studied in a lab using gas chromatography mass spectrometry (GC-MS) to determine the precise molecular makeup of odors, even those present in minute amounts.

A GC chromatogram is a visual output of the data recorded by the detector, and it is presented as a plot of detector response along the y-axis, versus retention time along the x-axis (See the graph in this article).

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Each compound detected appears as a single peak on the graph, with the corresponding retention time value used for identification. Once the odor-causing compounds are identified, scientists develop a formulation using plant oils to molecularly neutralize the odors when the additive is combined with the mix.

This results in versatile and cost-efficient solutions—specially crafted for maximum effectiveness in each application—with each solution leveraging customized concentrations of plant oils, biobased surfactants and water to eliminate odors. These additives are designed to be safe, non-toxic and biodegradable, and to be applied during any phase of the asphalt lifecycle: manufacturing, storage, transportation and use. When used in refineries, hot mix plants, transportation systems and paving operations, they are blended directly into the asphalt mix (Figure 3).

These additives are also useful for mitigating odors and blue smoke when dispersed via vapor phase during the capture of particulate matter in a baghouse.

Airborne vapor phase dispersion is also commonly deployed to control odors at storage terminals, where asphalt is kept prior to delivery.

Multi-mix odor neutralization with a single additive

One longtime Ecosorb end-user customer—a new and reclaimed asphalt pavement plant producing 1,500-2,000 tons of hot mix asphalt each day for contractors and construction firms—relied on a basic odor-mitigating additive for years. However, recent asphalt mix variability spurred the need for a specially targeted formulation. The different mix sources and grades began producing pungent odors in the areas surrounding the plant, and the standard additive was no longer effective.

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The plant shipped samples of three different asphalt mixes to Ecosorb’s lab to assess the levels of hydrogen sulfide, mercaptans and general hydrocarbons in each. The data from one asphalt mix, before and after treatment at 150°C is shown in Table 1.

Although the levels were different in each mix, the team of scientists formulated a single blend to neutralize odors in all three mixes, eliminating the burden of correctly matching different additives with a specific mix. The plant added this single blend to all its mixes, which reduced airborne sulfurous release by over 90%.

Ecosorb uses GC-MS instrumentation to identify odor-causing substances in asphalt mixes, and then develops custom plant-based formulas to neutralize odors.

Effective eco-products enhance odor abatement

By adding plant-based odor removers to asphalt mixes, manufacturers can effectively mitigate odors using safe, environmentally friendly and cost-efficient methods. These custom formulations do not mask smells, but instead mitigate them by breaking down and neutralizing odor-causing molecules in the mixes.

These mitigation techniques empower asphalt manufacturers to redirect their time from odor control and complaint handling, to maximizing production and overcoming the steady stream of challenges posed by evolving feedstocks.

Laura Haupert, Ph.D., is the chief scientific officer for Ecosorb, where she leads research and development, regulatory, safety and quality control. She earned her B.S. in chemistry from Manchester College and Ph.D. in physical chemistry at Purdue University, working with bond energies of solvated clusters. Haupert also completed her post-doctoral research at Purdue.