Cement handling & storage the right equipment for the job

Another energy-saving development is the piston return reservoir. During the air cannon’s firing sequence, the return reservoir’s canister pressure approaches that of the tank, but the fast-acting valve closes with about 50% of the tank’s original pressure remaining. The peak force output remains the same, but air consumption is dramatically reduced, easing the demand on plant air supply and saving money.

Air cannons have also become safer in recent years, with new positive-firing valves that respond to an air pressure surge delivered by a solenoid valve. This improves air cannon safety, as discharge requires a positive signal. Unlike negative pressure-firing designs, a cannon equipped with this type of valve will not discharge accidentally in response to a drop in pressure, so an air supply failure or broken line cannot trigger it.

In fact, researchers now believe that recent innovations have pushed the performance of air cannon technology near its physical limits, with valve cycles measured in milliseconds and efficiency at an all-time high. For this reason, more R&D effort is now being directed at the nozzles themselves, which create the air pathway that actually contacts the accumulated material. Manufacturers are finding evidence to support the hypothesis that new nozzle designs still hold significant potential for improving overall effectiveness, particularly in applications with difficult materials or extreme operating conditions.

NOZZLE DEVELOPMENT

The cement industry is an excellent proving ground for air cannon technology, as it presents such a demanding operating environment, including extreme temperatures and abrasive materials that affect nozzle wear and service life. It’s also one of the industries in which air cannon technology is most widely used, helping to solve accumulation problems in preheater towers, furnaces, clinker coolers and storage vessels. Yet the air cannon itself is just one component of the solution.

As the evolution of cannon and valve technology nears its logical limits, researchers are beginning to focus more on nozzles as a way to improve system performance, better customizing blast patterns and forces to suit the materials and process conditions of individual operations. The nozzle is the component that takes the stored energy in the form of compressed air and directs it to do work, so it has a dramatic effect on the performance of any air cannon. The application dictates the type of performance needed, including the shape of the air blast, length of the plume, etc. In addition to dislodging accumulated material, a goal in every application is to use the stored energy as efficiently as possible.

There has been some advancement in nozzle technology for air cannons over the last few years, such as a 360o retractable design that extends into the material stream only during the firing cycle to protect itself from extreme temperatures and abrasion. This innovative design solves two common industry problems: effectively dislodging accumulations in hard-to-reach areas without shutdown or manual labour, while significantly extending nozzle life. Further, the retractable nozzle can be serviced from outside the vessel, reducing service time and risk of injury.

For the most part, however, air nozzles used in today’s high- performance cannons are much like the designs used 20 years ago. Manufacturers offer a range of shapes, sizes and blast patterns to accommodate different materials and process conditions, but nozzle styles and performance have not changed significantly. Even after its long service history as a material flow technology, air cannon users still have a relatively small inventory of nozzle choices for high-temperature applications.

CFD MODELLING

Among the obstacles to new nozzle development has been the lack of precision in existing mathematical models for predicting the performance of new designs, particularly with respect to specific materials or conditions. While existing Computational Fluid Dynamics models could simulate nozzle performance in theoretical terms, the results often varied from the actual performance observed in a customer’s process. In addition, prototype manufacturing has traditionally been time-consuming and expensive, further slowing the R&D process. Selecting the optimum nozzle for specific customer operating conditions often took multiple iterations, making subtle changes to obtain the most effective configuration for that operating environment.

With the recent advances in numerical flow simulation software and the advent of rapid prototyping techniques, Martin Engineering researchers felt the time was at hand to create a more accurate standardized model and focus on designing new and innovative nozzles to further enhance air cannon performance. The objectives included development of a predictive theory that better reflects actual performance, accelerating the process from concept to prototype and drastically reducing trial-and-error tactics.

If successful, the result would be more effective cleaning performance from air cannon systems, with nozzle designs tailored to individual operating conditions. It was expected that engineers would also develop a deeper understanding of customer processes and foster product development that would be truly process-oriented. The benefits would include current product optimization, cost savings and faster development times, ultimately giving customers a virtually unlimited portfolio of nozzle options.

The investigation began with off-the-shelf software and CFD theory. Researchers plugged in the physical parameters of existing Martin Engineering nozzle designs and computed a projected blast pattern for each one. The nozzles were then taken to a test station known as a blast table, where they were mounted on a cannon and aimed at a horizontal surface covered with sand. By firing the cannon across the sand, investigators could obtain an accurate representation of the actual pattern for each nozzle design, which was then compared to the area of influence predicted by the software.

Following this series of tests, Martin researchers then revisited the CFD modelling program and made progressive adjustments, eventually resulting in a model that accurately reflected the blast patterns of the company’s existing nozzle shapes and sizes.

Armed with this customized model, investigators then turned to the development of new nozzle designs which could be tailored for specific customer operations and process conditions.

By progressing beyond a standard range of nozzle configurations from which the best-available solution would be chosen for a given application, the objective was to develop the ability to efficiently design and test nozzles developed specifically to suit individual customer processes, thereby delivering more effective cleaning under virtually any circumstances. Further, the customized CFD model will allow the R&D staff to accurately predict the forces and blast patterns resulting from any new nozzle design, without resorting to the expensive and time- consuming process of prototyping and physically testing every one.

FIRST DEVELOPMENT

The first nozzle development project using the new CFD modelling technique was initiated to address one of the most common problems shared by high-temperature air cannon users.

Replacing a conventional fan nozzle on existing equipment requires the removal of refractory brick from around the nozzle opening, typically with a pneumatic hammer. The process invariably weakens the surrounding refractory and renders it more susceptible to spider-webbing and subsequent cracking. The air cannon is disassembled from the air supply pipe from outside the vessel, and the failed nozzle is cut from the vessel or pipe, usually with a torch. The new nozzle is welded into place, and the damaged refractory is patched as well as possible, followed by the re-installation of the cannon outside the vessel. In addition to the potential refractory damage, the process is labour-intensive, requiring an extended system shutdown, and also introduces the risk of injury from working in a confined space. A key issue is the chance of misplacement, as even a pitch of just 1–2° can significantly affect a cannon’s effectiveness.

In contrast, traditional pipe nozzles can typically be changed from outside the vessel, without a need to alter the refractory inside. The cannon is removed from the pipe, and the nozzle can be drawn out through the vessel wall. Unfortunately, pipe nozzles have a smaller area of influence and are generally unable to deliver the same cleaning action as a fan jet nozzle. So Martin Engineering researchers went to work on designing a type of hybrid, one that would deliver cleaning performance equal to standard fan jets, yet be as easy to remove and replace as a pipe nozzle.

Using the modified CFD model, the R&D staff conducted virtual testing on several different nozzle configurations, continually refining the size, shape and orifice to investigate the changes in blast pattern. By eliminating the need to

prototype and physically observe each design, researchers were able to quickly narrow down the most likely candidates to a very small list. They were able to examine the predicted performance in detail and prototype only those which had shown the most promise in the CFD simulation, greatly increasing the likelihood of success during physical trials.

The patent-pending quick-change nozzle design that evolved from that investigation proved that the R&D team could achieve fan jet performance and combine it with the quick access which in the past had only been available from a pipe nozzle. The CFD model had been demonstrated in a real-world situation, helping the R&D team solve a problem that has confronted air cannon users (especially cement manufacturing operations) for years.

The benefits are expected to include significantly reduced damage to refractory brick and drastically shorter nozzle service times. By avoiding the need for confined space entry, the new design has eliminated much of the potential risk involved with the changeout process. It also allows system operators to add air cannons to an existing process during a brief shutdown, without completely cooling down the entire system to allow entry into the interior of a vessel.

In addition to helping researchers solve a specific problem, the process of developing the quick-change nozzle design and field-proving its effectiveness confirmed the utility and accuracy of the customized CFD model. The Martin R&D team now has confidence that they could approach any process experiencing particle accumulation issues and quickly design and manufacture a nozzle to deliver the optimum blast pattern for that specific application. No longer will air cannon users be limited to off-the-shelf choices or lengthy development times to test new designs. The customized software can be used to predict the blast pattern on an unlimited array of variations, and prototyping can be confined to the very limited number of configurations that best suit the individual process at hand.

CONCLUSIONS

The benefits of specifying high-efficiency air cannon systems networks for cement manufacturing can include lower energy costs, reduced maintenance, improved safety and greater total output. As the evolution of cannon and valve technology nears its logical limits, researchers have turned to the nozzles themselves as the next opportunity to enhance air cannon performance.

By customizing existing computational modelling software, Martin Engineering researchers have developed and confirmed an accurate method of predicting nozzle performance under specific operating conditions, allowing the company to develop nozzle designs for optimum effectiveness, while significantly reducing time-to-market. In fact, Martin Engineering researchers have already used the model to project the performance of hundreds of new nozzle designs.

Martin Engineering supplies bulk material handling equipment around the world for a wide variety of applications, including mining and coal handling, biomass, cement/clinker, rock/aggregate and other materials. Founded in 1944, the firm is headquartered in Neponset, IL, offering manufacturing, sales and service from factory-owned business units in Brazil, China, France, Germany, Indonesia, Mexico, South Africa,Turkey, India, the UK, Japan, Russia, Peru and under exclusive licence with ESS Australia.

A major contract was signed recently by AUMUND India to furnish all the necessary equipment for a second production line at the Wonder Cement plant at Nimbahera in India. The contract worth €5 million includes 32 individual machines from the AUMUND product portfolio.

Due to the ongoing very successful and reliable cooperation in servicing and supplying Line I at Nimbahera, AUMUND India was invited to tender for the installation of Line II. A convincing proposal was compiled within only five days. After short and intensive negotiations, Raju Gupta (managing director of AUMUND India) and Ibrahim Ali (director of Wonder Cement) signed a contract in June 2014 at Udaipur, India, permitting AUMUND to supply all machines needed for the construction of a second production line at Wonder Cement’s plant located at Nimbahera, District Chittorgarh within the Indian state of Rajasthan. The second production line will increase the plant’s capacity from 3.25mt (million tonnes) per year up to 7mt per year.

The scope of supply includes six chain bucket elevators, six belt bucket elevators, seven deep pan conveyors and 13 silo discharge gates. The chain bucket elevators included four double bucket elevators with two designed for a capacity of 1,775tph (tonnes per hour). Similarly, in the belt bucket elevators, the preheater feed elevators have a centre-to-centre distance of 150 metres, handling a capacity of 800tph. A reversible deep pan conveyor of a length of 162.3 metres is also part of the scope of supply. Beyond the delivery and installation of the machines, it includes supply and maintenance services for the future.

Wonder Cement is part of the RK Marble group which is one of the leading names in the marble industry. Its cement plant produces cement in line with international quality standards. The entire design of the plant is based on the latest environment norms, keeping emissions clearly below maximum permissible values.

ABOUT THE AUMUND GROUP

The largest American-owned cement manufacturer in the nation has solved a build-up problem in the precalciner of its Nebraska plant by installing a network of high-performance air cannons, improving material flow and drastically reducing the need to hydro-lance. The series of 25 air cannons from Martin Engineering fires a powerful discharge of compressed air in a prescribed pattern to remove material that becomes adhered to the vessel walls. The solution helps the plant avoid downtime and eliminate the potential for water blasting to cause lumps of material to fall into the kiln feed and interfere with production.

Ash Grove Cement is the sixth-largest producer in the US, with nine manufacturing plants, two deep water import terminals and a major quarry operation in Blubber Bay, British Columbia. In all, the company has a total annual capacity of nearly 9mst (million short tons) of cement, including a wide range of specialty products for difficult service environments. Located on the south bank of the Platte River between Omaha and Lincoln, the facility in Louisville, Nebraska has an annual output of about 1mst per year of Portland and blended cement.

When system operators began noticing material buildup in the precalciner, they found that it was impeding the flow through the preheater and into the kiln. The staff used the common technique of water lancing to remove blockages, particularly from the preheater tower’s riser duct. But the time-consuming process had to be repeated twice daily, when maintenance personnel would open access doors into the tower and remove the accumulation with a high-pressure spray.

AIR-POWERED SOLUTION

In order to prevent the loss of efficiency and clinker quality at Ash Grove Louisville, a group led by process engineer Mark Junkins investigated possible solutions. They met with material handling experts from Martin Engineering, and together the group designed a network of Martin® XHV air cannons for the main production line.

Martin Engineering technicians installed the air cannons during a scheduled maintenance outage, starting where the accumulation appeared most severe: below the riser orifice, where the duct is reduced in size to increase velocity. The unique cannon design requires no high-temperature discharge pipes or special mounting plates, and discharge nozzles are embedded directly in the refractory lining of the preheater tower.

All of the air cannons in the main production line network are equipped with the Martin Engineering XHV Valve, designed specifically to deliver premium performance and long service life in preheater towers, clinker coolers and other high-temperature applications. The negative pressure-firing valve was developed to provide reliable operation and long service life in challenging applications.

The cannons discharge in a timed sequence that moves in an upward spiral around the tower firing about 20 seconds apart, with the entire cycle taking just over eight minutes to complete. Control room operators can alter the schedule to accommodate a range of kiln pressures and operating conditions, extending the sequence to as much as 45 minutes.

A crew from Martin Services installed the entire system, including cannons, air lines and controls, as well as the company’s Thermo Safety Shields on each unit. Operating like trap doors, the sliding shields bolt in between the air cannon valve and mounting flange, helping to protect workers from exposure to severe heat, gases and high-temperature materials.

STAGE II

Based on its success with the initial air cannon system,Ash Grove started planning a similar system for the plant’s second 

production line. For that operation, engineers designed a network of 15 additional air cannons, equipped with Martin® Tornado exhaust valves. Described as the latest advancement in air cannon valve design, the patent-pending Tornado fires in response to a positive air pressure surge delivered by a solenoid valve, which can be located as far as 200 feet away.

The unique design improves air cannon safety, since the discharge sequence requires a positive signal. Unlike negative pressure-firing designs, a cannon equipped with the Tornado valve will not discharge accidentally in response to a pressure drop, so an air supply failure or broken line won’t trigger its firing. In addition, this positive- acting valve amplifies the discharge force, delivering up to 20% greater force than a standard XHV-equipped air cannon of the same size.

RESULTS

With the new air cannon network in place, the Louisville plant has been able to significantly reduce the need for water blasting. Material now flows more efficiently, and maintenance personnel have drastically reduced the man-hours that were spent on manual removal.

“We still hydro-lance occasionally, because of changes in raw material or fuel,” Junkins explained. “But we don’t have the issues we had before. We can see that the air cannon system has paid for itself, by allowing us to maintain production rates without many of the interruptions and issues that water blasting created.”

Ash Grove Cement Company has established a long-standing tradition of service, reliability and quality that stretches back more than 125 years. A pioneer of the lime and cement industries, the company was incorporated in Missouri in 1882 as the Ash Grove White Lime Association.

This article gives an insight for the criteria for the design of the plants for raw materials handling, storage and homogenization in the cement industry. The raw materials influence the investment in the plant due to the design and selection of the equipment. The important factor to note is that the cement process requires the raw materials to be prepared in a certain condition which could be in variance to the available materials.

Tenova TAKRAF has engineered solutions for cement plants across India. For instance, a cement plant’s most important raw material, limestone, may have vastly varying physical and chemical properties depending on the mine. In such cases the material needs to be blended together (often referred to as ‘homogenization’) over a time so that the variation of properties has minimal effect on production. It is imperative for the system designer to come up with tailor-made solutions for each and every application.

HANDLING AND STORAGE WITHOUT HOMOGENIZATION

Since blending is not a requirement, the scraper reclaimers operate on the principle of lateral reclaiming. The scraper arm makes a small cut on the sloping face of pile and the reclaimer travels over the length of the stockpile. This process can be fully automatic with active controls for depth of cut and travel speed to regulate the output from the equipment. The type of scraper can be either side (cantilever), half portal or full portal.

These scraper reclaimers do provide a minor blending effect since the cones are sliced uniformly during the travel. However, the greater benefit comes out of the flexibility of the equipment, since the travel of the machines in the store is not hindered by the presence of stockpile. This is useful for the cement plant when handling different materials from the same set of stacker and scraper reclaimer or when the process demands different grade of the same material.

HANDLING AND STORAGE WITH HOMOGENIZATION

Good homogenization is provided by the chevron method (Fig. 4) of stacking enabled by a fully automatic control system. The linear stacker moves over the length of the stockpile forming several layers (may be hundreds) over one another. The end cones with predetermined stacking procedure give correction to the extent possible. To diminish the effect of end cones on the product, it is advisable to have a pile configuration having length to width of minimum 4:1. The end cone effect can be completely eliminated in case of continuous stockpile in the circular pre- blending system.

Cargotec’s Siwertell has received an order from CITIC Heavy Industries Co Ltd (CITIC) for a rail- travelling ship unloader. CITIC is one of China’s largest conglomerates, headquartered in Luoyang, Henan province.

The ST-640 M-type unloader has been ordered to support the energy production requirements for a new cement production facility in Burma/ Myanmar and will unload coal from barges at a rate of 800tph. The facility is being built as part of a collaboration between CITIC and the Thailand-based Siam Cement Group subsidiary, Mawlamyine Cement Ltd (MCL). CITIC states that the new production plant will have a cement capacity of 5,000 tonnes per day.

“This order has special commercial significance for Siwertell as it will be the first delivery to Burma/Myanmar,” says Ola Jeppsson, Siwertell sales manager. “MLC will benefit from all the excellent attributes of our Siwertell unloaders including efficiency and quiet, safe, environmentally-friendly operations without dust or spillage. “A Siwertell screw-type unloader was the preferred solution for the new Mawlamyine cement plant. Siwertell screw-type unloaders lead the industry and have decades of operational experience and numerous favourable global references.

“The low weight of the unit when compared to alternative unloading systems minimizes loads on the jetty and so reduces jetty construction costs,” Jeppsson adds.

The delivery is scheduled for mid-2015, and will include an enclosed discharge arrangement for transferring coal to the jetty conveyor. The unloader will be delivered in pre- assembled parts, with final assembly, testing and commissioning taking place on site at Mawlamyine.

CLEVELAND CASCADES TANKER LOADER SYSTEMS SUCCESSFULLY COMMISSIONED AT TITAN CEMENT, HULL, UK
Titan Cement UK, based in Hull, recently invited Cleveland Cascades Limited to commission two tanker loader systems purchased earlier in 2014 at King George Dock. The chutes load cement into tanker trucks with closed hatches at rates of up to 150tph (tonnes per hour). The cement is imported from around Europe on vessels, and is air-blown into Titan Cement’s storage silo for truck-loading thereafter. The Cascade tanker units utilize a rubber seal at the outlet in order to create a perfect seal between the chute and the tanker hatch for much improved dust-free loading. The air displacement is controlled by an internal extraction system that works across both chutes and any product extracted is taken back into the silo for re-loading.

“While cement is as vital a commodity to fast-growing economies as oil or steel with no other material being as versatile for building houses, roads and infrastructure, it is difficult to transport and potentially polluting if not stored and transported carefully,” says Paul van de Vyver, general manager of DemcoTECH Engineering.

As a key supplier of bulk materials handling technologies and services to the cement manufacturing and related industries, South Africa-based materials handling specialist DemcoTECH Engineering offers the global industry a complete solution for the storage and transportation of cement.

CONVEYOR DESIGN

“As with all the commodity markets we serve, maintaining a clean environment is a priority in all the systems we design and supply to the cement industry,” notes van de Vyver. “As a result, we offer specialized conveying systems, such as troughed AeroConveyorsTM, pipe conveyors and pneumatic conveying systems, which, by providing a totally enclosed conveying environment, assist the client in complying with environmental and safety regulations.

“What makes the AeroConveyorTM system unusual is the fact that it uses the air-supported belt principle to convey bulk materials, with air being used in much the same way as for a hovercraft, i.e. as an air cushion as a means of transport, eliminating the requirement for idlers.”

Although similar to the conventional idler-supported conveyor system, a trough section is used as the structural support of the belt on an air cushion. “Air, a natural resource is used successfully as a substitute for idlers, yielding substantial benefits, including an economical-to- construct-and-operate conveyor and one that has very few moving parts, thus requiring very little maintenance.”

DemcoTECH Engineering offers specialist expertise in pipe conveyors, having supplied this technology to a number of cement producers around the world. Besides secure handling of the material, pipe conveyors offer many other benefits, such as being environmentally friendly without the spillage problems associated with troughed conveyors. Pipe conveyors are able to negotiate relatively tight horizontal and vertical curves, which affords the opportunity to eliminate transfer points, reduce the overall length of the conveyor system and improve the plant footprint, and save total costs.

“The potential conveying distances and carrying capacity of pipe conveyors have improved significantly in recent years due to improved conveyor analysis capabilities and advances in component design, to the extent that pipe conveyors today offer clients a realistic alternative to conventional troughed conveyors,” highlights van de Vyver.

Pipe conveyors designed by DemcoTECH Engineering comprise both fabric and steel cord belting, have up to 2,250 tph conveying capacity and are up to 500 mm in diameter. “We have also engineered two-way pipe conveyors, multiple curve pipe conveyors and distributed drive pipe conveyors with excellent results,” says van de Vyver.

Two such travelling maintenance trolleys were designed by DemcoTECH Engineering for a cement producer, each equipped with maintenance power sockets. These maintenance trolleys had to negotiate an incline of up to 15° while carrying four personnel together with spares and tools.

DemcoTECH Engineering’s track record in supplying pneumatic systems for the cement industry includes a 150tph (tonnes per hour) pneumatic transport system to convey cement from a kiln to multiple storage silos, also at Nova Cimangola’s cement plant in Luanda.

“Working in conjunction with Claudius Peters in Germany, we provided a system with a conveying distance of over 300m, following a tortuous route to fit into the existing plant and including seven discharge points into the existing silos.”

CEMENT SILO DESIGN

DemcoTECH Engineering offers the full suite of services and technologies for the design and construction of cement and clinker silos in partnership with Kantey & Templer Engineers. All equipment complies with environmental and safety requirements and typically includes airslides, flow-control gates, mobile road outloaders, fully-enclosed cement transport/conveying systems, and dust filters, which provide effective removal of dust from all the areas of dust generation.

DemcoTECH with Kantey & Templer completed the new 40,000-tonne capacity, multi-discharge clinker silo at NPC Cimpor’s Simuma Plant in KwaZulu-Natal, South Africa on a turnkey basis.

“The Simuma Cement Plant is located in an environmentally sensitive area and the design ensures that dust emissions from the plant are controlled well below regulatory requirements,” says van de Vyver. “Dust extraction filters are included on the silo and at all the transfer points to ensure the dust emissions comply with the safety and health regulatory limits.“

ABOUT DEMCOTECH ENGINEERING

DemcoTECH Engineering is a specialist in the bulk materials handling field, offering its clients a range of services from concept to full, turnkey project completion.

DemcoTECH Engineering offers clients conveyor design through to turnkey supply and has completed the design and engineering of large import/export port facilities, gold plants, diamond tailings disposal systems, manganese storage and export facilities, sampling plants and a wide range of other projects including niche process plants. Services include concept design, feasibility studies, detail design, engineering, procurement, expediting, construction and commissioning for a wide range of industries, including the power generation, cement, mining, metallurgy and manufacturing industries, as well as port facilities.

DemcoTECH Engineering offer a full range of materials handling products and solutions including troughed conveyors, pipe conveyors, air assisted AeroConveyorsTM, rail-mounted slewing stackers, pivot-boom conveyors and mobile conveyors