Transporting household and industrial waste as well as sewage sludge from a treatment plant to a power station can be a messy business. The utility company Linz AG found that a pipe conveyor system offered an optimal solution. The conveyor is not only highly energy efficient, but due to its closed design, it also allows waste products to be conveyed through public spaces without affecting the environment.
Linz AG’s waste incineration power plant has been in operation since 2011. It is located in the industrial area of the port of Linz, Austria, built on the banks of the Danube next to an existing biomass power plant and the district heating plant.
The waste incineration plant generates district heat and electrical energy for the company’s networks. The utility company manages the entire waste removal process—from collecting to eco-friendly recycling. This helps Linz AG guarantee much higher supply security in its district heating network as well as adequate waste disposal.
A Coordinated Operation
Generating energy from waste and residual material incineration is a relatively efficient process. The steam produced can be used for heat or for turbine operation. Trucks, ships, and trains transport about 150,000 tons of household, commercial, and industrial waste to the residual material processing plant located on a neighboring property of the Linz tanker port.
Additionally, approximately 50,000 metric tons of dehydrated sewage sludge is processed in the wastewater treatment plant in the municipality of Asten, located 13 kilometers (km) away. The sludge and screenings are transported directly from the Asten plant to the power plant.
The highly efficient residual material processing plant sorts and shreds the waste, separating ferrous and non-ferrous metals and impurities. Finally, particles of 80 mm or less are transported into the 3,000-ton-capacity fuel bunker.
Material Transport Using a Pipe Conveyor
The residual material processing plant, and the heat and power plant are located several hundred meters away from each other. To complicate matters further, a public street is crossing the route. The safe transportation of materials has to be absolutely guaranteed. No waste, not even the smallest amount, can be allowed to fall on the ground.
The odor of the waste must not be a nuisance to people living in the area either. The people in charge of the project at Linz AG evaluated several different solutions for the bulk material transport. In the end, they opted for a pipe conveyor.
The pipe conveyor system not only protects the environment from falling items during transport, but it is also able to navigate long distances (Figures 1 and 2) and tight curve radii. Due to this characteristic, considerably fewer transfer towers are required compared to other belt conveyors (Figure 3). This allows for substantial cost savings for the customer, and the system can be easily customized to the individual routing.
|1. A long and winding road. Due to its ability to negotiate curves, the pipe conveyor system can be optimally designed for any plant layout. Courtesy: BEUMER Group GmbH & Co. KG|
|2. Going up? Relatively steep inclines can also be overcome using a pipe conveyor. Courtesy: BEUMER Group GmbH & Co. KG|
|3. Getting from point A to point B. Lenz AG’s pipe conveyor transports material from the storehouse across a public street to the power plant. The enclosed design prevents spills and eliminates odor emissions. Courtesy: BEUMER Group GmbH & Co. KG|
Similar to a conventional belt, the feeding area of the pipe conveyor is open (Figure 4). After a certain distance, which depends on the pipe diameter or belt width, special idlers mold the belt into the desired closed shape. From this point on, the closed belt runs along the entire conveying distance, through what are known as panels and partition plates.
Six rollers are installed in a staggered arrangement on each of these panels for the upper and lower strands. At the end of the conveyor line, the belt opens naturally and discharges the material. In the return strand, the belt is rolled back into its tubular shape.
Durable and Safe
The conveyor belts used are very durable and are specially manufactured for the pipe conveyor. The belt quality is selected depending on the application, conveying capacity, and length. For instance, a differentiation is made between normal, heat resistant, or non-abrasive rubber qualities. Steel cables or textile fabric can be used as the traction element, depending on the required belt strength.
The whole cross section is not used to transport material. The degree of filling is typically limited to approximately 75%, depending on the material to be transported. The percentage offers a safety margin in case there is a temporary increase in capacity, which needs to be balanced out.
There are safety devices that protect the conveying system against damage. One of them is the first panel after the belt forming station. These security panels are designed to be separable.
The pipe conveyor is a volumetric conveyor, that is, a system with a limited volume flow rate. This means that the load needs to be limited. If too much material, oversized particles, or foreign material is fed, the security panels open and release the belt. This prevents belt damage. The opening of the belt activates safety switches, and the pipe conveyor is immediately stopped.
To plan and establish dimensions for the pipe conveyor layout, the system parameters as well as the core components have to be determined and specified. The process- or operation-related requirements serve as entry data. Functional and operational reliability are the primary objectives when planning a system.
In order to assess the capital cost, decision-makers must consider not only the conveyor itself, but also all of the other cost factors that are determined, or at least influenced, by the design of the system. This includes the steel structure, the necessary reconstruction measures on the facility—such as on systems, buildings, or traffic routes—and earth works. The operational costs not only include the system operation, maintenance, and wear parts, but also energy costs and system availability. Use of standard components can minimize the project expenditure and risks.
Efficient waste disposal is a major concern today. High quantities of waste are accrued close to big cities. At the same time, these cities require power and heating supply. The combination of waste combustion for power generation close to big cities is an ideal solution, which is why these combined heat and power plants are often situated close to their consumers.
Pipe conveyors, however, are not used only for alternative fuel transport. They are also being installed for removal of combustion residues, such as fly ash or stabilized ash—both being generated in caloric power plants—as well as flue gas desulfurization gypsum. So the pipe conveyor application fits into various power generation processes. Additionally, the waste-to-energy process is not only used in the power business but also in other industries where cheap fuel is required for the production process, such as the cement industry.
Proven System Availability
Linz AG has been using a pipe conveyor with a center distance of 475 meters (m) for the last four years. It conveys up to 40 metric tons of material per hour. The system is running around the clock, seven days a week. Due to the system design and the required capacity, the pipe conveyor has a diameter of 300 mm. The difference in height between the feeding and discharging point is 24 m.
A big advantage of the pipe conveyor is the reduced noise emission that the system provides. This is achieved by using special idlers, low-noise bearings, and the correct conveying speed. This improves the quality of employees’ day-to-day work environment and ensures that people living near the conveyor line are not disturbed by the noise.
While conveying waste can be a messy business, using a pipe conveyor system has produced some positive results for Lenz AG—no material loss, no unpleasant smell, and most importantly, no pollution to the environment. ■
— Josef Staribacher is managing director at BEUMER Group Austria GmbH.