VIGAN compares the relative merits of pneumatic and mechanical CSUs
Major supplier of both pneumatic and mechanical continuous ship unloaders (CSUs) VIGAN has considered the advantages offered by each system, and has shared its conclusions with Dry Cargo International.
There are many different criteria to consider; some of these are key to making the right decision when acquiring unloading equipment.
Therefore, port operators or project managers must take the following factors into consideration.
AVERAGE EFFICIENCY AND HOLD CLEANING
The most challenging operational task for any ship unloader machine is its ability to clean the holds quickly.
As a general rule, the nominal capacity (also called design capacity), given in metric tonnes per hour, is fairly similar to the maximum capacity. This is usually measured somewhere in the centre and at the top of the hold.
The average capacity includes the whole unloading process, including the final cleaning of the holds. The average efficiency is the ratio in percentage between average and maximum capacities.
Because the mechanical and pneumatic CSU have different technologies for handling the products, the consequences will mainly be the following ones:
- pneumatic unloaders will be able to very efficiently ‘suck’ the product being unloaded, right down to the hold floor surface, as well as its corners. (They are basically ‘big industrial vacuum cleaners.) In practice, this means that pneumatic unloaders are often the first choice for the unloading of barges and vessels of any size. A lifting hoist with a capacity of more than 10–12 tonnes can be installed on the suction boom for auxiliary equipment in order to speed up the cleaning process even more.
- mechanical unloaders maintain a constant handling rate during 80–85% of the hold volume, leaving only 15–20% of the product in the hold for the cleaning operations. However, it is much more time-consuming to discharge this percentage remaining in the hold. This remaining layer is the height needed for the intake booth to be able to pick up products, and it typically 70–100cm deep. This means that a significant amount of product has to be fed to the intake device (screen, belt or chain type), usually using auxiliary equipment such as bulldozers.
For both categories of equipment, average efficiency is also influenced in a similar way by a range of factors. These include the size of the ship, the skill level of the workers operating the unloaders, restrictions from the ship’s captain, weather conditions, and so forth.
In practice, figures obtained from VIGAN customers indicate that average efficiency for pneumatic equipment is around 75% to 80%. For example, a detailed report in 2001 reported an efficiency of up to 80%, using a 12-year-old machine. More recently, in 2012, another customer reported an efficiency of 78.43% over 82 ships, using a ten-year-old machine.
The average efficiency of mechanical unloaders is lower, for the reasons given above. The graph above, showing performance with one mechanical and two pneumatic unloaders, confirms VIGAN’s own experience. VIGAN manufactures a popular mechanical CSU, the SIMPORTER, which uses twin-belt technology.
The graphs shows that, although the two pneumatic unloaders were helping the mechanical unloader with the cleaning, the average efficiency was only 65–70 %.
As in many other sectors, in recent years, there have been major improvements aimed at reducing power consumption.
For the CSU, the most significant ones are related to the speed variator technology (also called frequency inverters) and all the energy monitoring devices for the fine tuning of the engines and the other mechanical components in general.
Therefore, compared with 12–15 years ago:
- pneumatic equipment: the power consumption has fallen from 0.9 to 1.0kWh/t down to 0.6 to 0.8kWh/t;
- mechanical equipment: from 0.5–0.7kWh/t down to 0.35 to 0.45kWh/t.
ANNUAL COST COMPARISON
Both the average efficiency of the CSU, and its energy consumption, have significant impact on some annual costs.
The relative importance of the following aspects will mainly depend on the circumstances of each project, and the port conditions:
Total weight of the equipment
Old quays not designed for heavy equipment, or with debilitated structure, will require lower-weight equipment.
For a similar unloading capacity, pneumatic equipment weight will be around 40–60 % less in comparison with a mechanical one. Indeed, in most cases, the pneumatic machine will not require any counterweight for balancing the heavy weight of the vertical and horizontal steel structures as it is the case for the mechanical type unloaders.
When a new pier is being constructed, important savings can also be achieved with lower weight port equipment.
Ship size workable capability
The technical director of a major flour mill was asked: “After such a deep technical evaluation of both alternatives [mechanical or pneumatic], why did you choose pneumatic equipment?” He replied: “A most important reason, because it allows me to unload a wide variety of ship sizes, thanks to its vertical and horizontal telescopic pipes. This is definitively not the case with mechanical equipment, due to the rigidity of the intake arm and horizontal conveyor.”
Damage to the products: delicate cargoes
VIGAN pneumatic CSUs are able to discharge malt, rice cargo and cocoa beans: reports from very prestigious companies like Cargill, Heineken and ADM confirm that the high conveying speed in VIGAN pneumatic machines is definitively not causing any damage.
The twin belt technology (SIMPORTER machines), in comparison with chain or screw type CSUs, offers the advantage that products do not suffer any friction during handling by the belts, as the particles are static and caught between those belts.
This is a major concern today, and often companies proudly advertise their accident statistics at the entrance to their plants. A pneumatic suction nozzle does not have any running components, therefore the accident risk is non-existent.
Maintenance and repairs
Suction pipes do not require maintenance (no running parts!) and can be easily repaired: there is no need to dismantle a complex mechanical system.
Almost all maintenance can be done in the main engine room, which is easily accessible and therefore there is a higher probability that it will be carried out properly.
Risk of cargo residues (eventually fermented due to high humidity content) This is avoided in pneumatic machines because the large volume of air is continuously cleaning the pipes and the other components such as the filter bags for instance.
The most important factor is the lower CAPEX (capital expenditure: mainly the investment and financial costs) of pneumatic equipment, for the same handling capacity in comparison with mechanical unloaders. In the case of mechanical CSUs, energy cost savings are frequently ruled out by higher CAPEX figures.
Reliability in handling (confirmed by field reports from well- established and renowned customers), combined with up-to-date technologies using latest-generation components, result in low OPEX (operational expenditure).
Both CAPEX and OPEX figures are almost always in favour of pneumatic CSUs.
Nevertheless, the mechanical CSU can, under particular circumstances (mainly for high annual volume unloading operations), also be an interesting alternative. For large size projects or existing unloading facilities, the combination of both systems can offer the benefits of both technologies.
Bühler: the choice between pneumatic and mechanical depends on user needs
Bühler manufactures both pneumatic and mechanical equipment, so that it can offer the best solution to its customers according to their specific requirements.
Pneumatic unloaders, such as Bühler’s Portanova, are particularly useful in situations where the annual unloading volume is low, and overall efficiency is not of the highest importance. For customers with a high annual throughput, who expect high overall efficiency from their unloaders, mechanical unloaders — which are capable of higher capacities — can be a more appropriate solution.
Bühler’s equipment is used to efficiently handle free-flowing bulk materials such as grains, cereals, oils seeds, but also more complex and delicate products such as feed pellets. Moreover, Bühler unloaders also handle non-free-flowing products such as soya meal.
The company’s major clients include large grain terminals, which specialize in the loading or unloading of bulk material. Other major customers are large end users such as commercial mills, feed mills, etc. Bühler’s experience is that there has not been any significant
change in global competition recently, though the trend for purchasing unloaders from Chinese manufacturers does seem to have slowed. Although the initial investment costs for these unloaders is lower than that of loaders from companies like Bühler, unloading performance tends also to be lower. Therefore, higher costs-per-tonne, higher-than-anticipated maintenance costs and a generally lower quality of the installation all add up to a higher total cost of ownership. Bühler is highly specialized in the unloader market, and has a full product portfolio. The company has long experience in both pneumatic and mechanical technologies. It offers calculation tools to clients, to assist in making the right decision when acquiring equipment for an individual application. Further advantages offered by the company include the fact that the various components and machines used in an installation are all designed by Bühler, and built in such a way that they are a perfect match. Moreover, project managers are able to have an optimum overview of the process, with direct customer contact.
Bühler has been awarded a contract to install a Portanova in Bangladesh with a nominal capacity of 250tph (tonnes per hour) for the unloading of barges with a maximum capacity of 5,000dwt. In addition to the Portanova, Bühler will install a total silo with a volume of almost 100,000 tonnes and the mechanical equipment required.
GENERAL COMPANY BACKGROUND;
Bühler is a global technology expert which specializes in the supply of equipment, systems and services for the conversion of renewable resources derived from food and synthetic substances into top quality functional products and materials. Bühler operates in over 140 countries and has over 10,000 employees worldwide. In fiscal year 2012, the group generated sales revenue of CHF 2,409 million.
Bühler Grain Logistics delivers products and complete solutions for the entire value-added chain, from agricultural product collection points right through to food processing plants.
Why opt for a pneumatic system? Neuero has the answers
Neuero Industrietechnik asks why it is that a system that is safe, generates the lowest noise and dust emissions, completes the job including clean-up, is highly efficient and requires lower investment is not always the first choice.
The answer is simple, says Neuero. Many manufacturers do not invest in research and development, or have simply gone in the wrong direction, resulting in the loss of technical expertise. When big companies in the flour milling market do this, they argue that a pneumatic system is not the best choice. This can result in uncertainty from clients, even those that have used pneumatic systems for years.
Also, some manufactures make recommendations that are based on their product offering, rather than on the best interests of the clients.
Therefore, users’ decisions are made all the harder, and this can result in restrictions in the use of a system, based on erroneous assumptions. Neuero says that this situation can be rectified, by illustrating some real-life examples that illustrate technical innovations.
Neuero has invested in not only a new testing and research laboratory, but more importantly in technology. The result is a new turbo blower with direct drive. The result can be seen in a reduction in energy requirements while maintaining a high capacity.
The energy requirement has been is the only weak point in the pneumatic unloader compared with a mechanic unloader. The power requirement gap has been reduced with the new Neuero blower direct drive compared with older pneumatic technologies. This also gives the opportunity for Neuero to be active in refurbishing less efficient existing installations.
In addition to the energy reduction, reliability has also increased. The direct drive is now equipped with temperature and vibration sensors to monitor bearing conditions and provides a warning to prevent a bearing failure or notify maintenance to change it. The use of fewer parts also reduces the need for maintenance.
In addition to new installations in Russia, Egypt, Romania, Saudi Arabia incorporating the new Neuero blower direct drives,
Neuero is also giving a second life to older installations. The first is now in Damietta, Egypt where a 30-year-old shipunloader (not made by Neuero) reached its original capacity with the new blowers and conveying adjustments, while cutting power consumption in half.
Russia: two ship unloaders of 600tph (tonnes per hour) each for the biggest oil extraction plant in Russia. This is part of a third expansion at the site. Neuero has delivered two shiploaders for this project as well.
Damietta: this is interesting because here you can see the evolution in pneumatic shipunloading based on real comparison. The upgrade of the blower (see pictures on p66) is like carrying out a heart transplant, because many unknown factors need to be considered. Neuero has done several similar jobs with various manufacturers’ unloaders around the world, like in Iran, Philippines, Saudi Arabia and Oman.
The modernization of a competitor’s shipunloader built in 1985. There are two identical units installed in Damietta. Each dual line unloader was sold to have a nominal original capacity of 2 × 350tph. However, it has not been confirmed whether they ever reached this capacity in the past. The new goal was to get 300tph per line.
The main problem in any modernization project is to know in advance all the necessary parts that need to be replaced. This is normally not possible because of hidden problems that can only be detected after the replacement of key components. The bottleneck passes to the second phase.
In the Damietta project, in order to maintain the lowest investment cost, we installed only a new Neuero blower with direct drive on one line and tested using the original conveying piping. The second phase was to replace the old boom and piping and nozzle (see pictures above) as well as installing a new belt airlock. The results are shown in the table, right.
The results show what is possible with relatively low investment in existing installations to get back to original capacity with lower energy requirements. Here, Neuero developed the conveying pipes in Hardox 450 for a longer life and also supplied Neuero winches for the necessary movements.
The capacity of 350tph was reached for short periods of time.
For example, a new ship unloader designed today to reach the capacity of 350tph, a 330kW motor is installed and less than 300kW consumed. This gives a power consumption of 0.80kW/ton.
WHY IN THE PAST WAS MORE ENERGY NEEDED?
There are many possible answers to this question. First, the use of rotary piston blowers requires more energy. Second, most manufacturers do not design the unloader around the customer’s requirements. They use their existing designs and parts and try to adapt instead of engineering a product for the application.The result is to supply what they want and not generally what is the best for the customer or the application considering energy optimization and maximum unloading capacity.