Chapter 6: Logistics and storage room for wood pellets

Transcription

1 Chapter 6: Logistics and storage room This chapter deals with the demands of the transport and the storage of wood pellets. Content 6. Logistics and storage room Introduction Requirements for the delivery of wood pellets Demands on an interim storage room Demands on vehicles to transport wood pellets to the consumer Checklist Storage room for pellets Positioning of a pellets storage room Dimension of a fuel storage room fuel requirements Structural requirements Injection nozzle and pipes Access to the storage room Buried tanks Storage container 11

2 6. Logistics and storage room 6.1 Introduction Wood pellets are sold either in packs, mostly bags of 15 kg, or in bulk. Logistics concerning the packages is similar to that of wooden briquettes. The collection of the bags from do-it-yourself-stores, supermarkets, retailers and petrol stations can be done by the customer himself or a delivery on pallets can be organised. Wood pellets in bags shall be kept dry. Due to the waterproof synthetics these bags are made of, a temporary intrusion of humidity will be no problem. But for a long term outdoor storage they are not suitable because the packing will not resist a longer exposure to the elements. The delivery of wood pellets in bulk requires adequate logistics including suitable interim storage facilities at producers or retailers, appropriately equipped vehicles for delivery (silo vehicle) and a professionally built storage room. To guarantee the quality of pellets certain standards of transport, interim storage and the storage at the customer have to be fulfilled. Solid biomass should not be contaminated with sand, soil, waste etc. And of course it has to be protected from humidity. Due to the firing system and the materials handling technology, the highest demands are made on wood pellets, compared to the easy logistics and storage of logwood. Therefore, a national corpus of legislation was created to support everybody, especially pellets producers, carriers and retailers, to avoid mistakes and achieve customer satisfaction: ÖNORM M 7136 Compressed wood in natural state quality assurance in the field of logistics of transport and storage ÖNORM M 7137 Compressed wood in natural state wood pellets requirements at the storage of pellets at the consumer Carriers and retailers who comply with the ÖNORM M verified by an independent body are awarded with ÖNORM M 7136 certified. 6.2 Requirements for the delivery of wood pellets The fuel identification has to be mentioned in every document in the order form, the delivery receipt and the invoice. In Austria the retailer/carrier must verify that he only delivers wood pellets which are HP1 ÖNORM M 7135 certified. Regarding pellets certified according to different certification marks as for example the German DINplus or the Italian Pellet Gold these types of certification marks can be regarded as equal. Wood fuels, especially wood pellets, must be stored and transported separately from other fuel types. A blending of pellets of different quality or diameter is not allowed. Seite 2

3 Vehicles for the transport including all the facilities (e.g. covers) have to be cleaned carefully. Solid biomass for small-scale consumption, especially wood pellets, has to be kept dry on the whole way from the production to the combustion Demands of interim storage room Wood pellets must be stored in a completely closed storage room; the surface of the ground must be a granular sub-grade course (e.g. concrete, asphalt). A closed silo would be another possibility. The most important requirement for storing wood pellets is to keep them dry. Direct exposure to rain, snow and wet walls has to be avoided. Any areas where pellets are handled have to be roofed. All the areas used to store and to handle the pellets have to be clean (e.g. no soil, sand or stones) Abb. 1: Example for large-scale storage of wood pellets Source: ofi Österreichisches Forschungsinstitut für Chemie und Technik Seite 3

4 6.2.2 Demands for vehicles used to transport wood pellets to the consumer Due to the mechanical load of the pellets the fine fraction is allowed to rise by only 1 % between the production and the arrival at the consumer. During the air injection it is again allowed to rise by 1 %, consequently the fine fraction in the storage room of the consumer can be 3 % maximum. Vehicles to transport wood pellets with a payload more than kg must have a calibrated on-board scale. Furthermore, it must have the equipment to expel the injected air from the storage room. The air volume of this equipment must exceed the air volume of the compressor for the air injection. Gauging pressure in the storage room should not be possible. The standard equipment on the vehicle to transport pellets shall include a flexible tube with 30 m length minimum as well as appropriate adapters and couplings. When a longer flexible tube is necessary the supplier must be contacted. If the distance for the air injection greatly exceeds 30 m the mechanical load of the pellets increases because of a necessarily higher pressure during the injection. Besides, the conveyor capability decreases and the injection can last much longer than normally. To avoid this problem the distance for the air injection should be considered when building the storage room. (see 6.3.). Abb. 2: Example of a silo vehicle Source: ofi Österreichisches Forschungsinstitut für Chemie und Technik The air injection can as well be applied to wood chips G30. There are no requirements for vehicles transporting wood chips. Therefore, it s recommendable to discuss the technical requirements with the supplier. Seite 4

5 Coarse wood chips and log wood are usually tilted, log wood is offered as well in do-ityourself-stores on pallets of 1m³ Checklist The supplier has to fill in the checklist before every delivery to the consumer, it has to include the following issues: Heating off: YES/NO Storage room closed: YES/NO How much and which kind of fuel remained in the storage room Used length of tube in m Miscellaneous remarks (e.g. no impact protection, aggregation of dust). The checklist has to be part of the delivery documents and can be integrated in the delivery receipt. 6.3 Storage room for pellets The demands on storage rooms for pellets are described in the ÖNORM M Storage rooms for pellets are aimed for functionality, they must comply with the requirements concerning operational safety, fire protection, static demands, and conservation of the pellet quality Positioning of a pellets storage room Precautions should be taken that allow the vehicle to drive as close as possible to the injection nozzle in order to avoid a deterioration of quality of the pellets through the mechanical load during the injection. A distance of 30 m maximum is strongly recommended, silo vehicles are equipped with a tube of 30 m length according to the standard. If it s not possible to meet the suggested 30 m distance, the air injection could impair the quality of the pellets. With a distance of more than 30 m to the injection nozzle the supplier must be advised to supply the necessary tubes. The access route must be suitable for the transport vehicle. For heavy goods vehicles a road of 3 m width minimum and a vertical clearance of 4 m minimum is necessary. Seite 5

6 Abb. 3 Positioning of a pellets storage room Source: ÖkoFEN Pelletsheizung Dimension of a fuel storage room fuel requirements The storage room should be big enough to hold the fuel demand for one heating period. A fuel requirement of 0.6 m3 to 0.7 m3 pellets per kw heating load for one heating period in Austria can be assumed. 1 m3 pellets correspond approximately to a mass of 650 kg. The heating load can be calculated according to ÖNORM M 7500, in addition it can be found in the new Energy Performance Certificate. Every 2 or 3 years the storage room should be discharged completely and cleaned of fine particles and dust Structural requirements Walls and supporting parts shall be able to carry the static load. In a 2.5 m high room pellets with a bulk weight of approx. 650 kg/m³ can put high lateral pressure on the walls. The storage room must guarantee to prevent the ingress of moisture during the storage and the filling. Furthermore the formation of condensation water must be prevented (e.g. Seite 6

7 on exposed water pipes). Pellets are also able to absorb air humidity, therefore the storage room should not be ventilated. All the electric, water, waste water or other installations must be passed in-wall or they can be well insulated and protected from mechanical load. In addition they have to be installed according to fire protection requirements (TRVB H 118 as well as other particular regulations and laws). For reasons of safety in the storage room no exposed electric installations (lamps, wires, distribution boxes, sockets, light switches etc) are allowed The storage room must be built as dustproof, that means the door to the cellar/central heating room needs a sealing. If the low pressure is not granted during the whole procedure of filling the room, air mixed with dust will intrude in the cellar and the whole house. The accessibility of the storage room must be guaranteed in such a way that necessary tasks of maintenance and cleaning can be done. The plan of an ideal storage room is rectangular. The nozzles for injection and extraction should be positioned on the shorter side. If possible an outer wall with the nozzles should be integrated in the room. Due to the technical equipment, floor inclines, and delivery systems, normally only two-thirds of a storage room can be used as filling volume for the pellets. Abb. 4: Top-View of a pellets storage room Seite 7

8 The installation of an abrasion-resistant and tear proof impact protection is obligatory. It should be attached either at a right angle to the direction of injection or on the opposite wall. A HDPE film with 1 mm thickness and a size of squared 1.5 m has proved its worth as impact protection. The funnel-shaped floor (see pic. 5) must have an inclination of 40 minimum. Exposed to static load it must not deform and it must have an even and abrasion-resistant surface. (e.g. DOKA-Platten = DOKA-Slab floor coated with melamine resin or a hardboard with the even surface up). The occurrence of webs and edges on the transition to the funnel/delivery system should be absolutely avoided, but that s a mistake that is often made. On the one hand, fine particles can concentrate in these edges and fall down from time to time. Then these conglomerated particles can block the screw conveyor. On the other hand, edges enhance the formation of bridges, which can cut off the fuel feed. Abb. 5: Sectional drawing of a storage room and funnel floor Seite 8

9 6.3.4 Injection nozzle and pipes The nozzles for injection and extraction should be indelibly and distinctively labelled. The length of the storage room measured from the injection nozzle must be declared on an identification plate near the nozzles. Both nozzles must be installed in one wall within a distance of 20 cm minimum under the ceiling (measured between ceiling and the top edge of the pipe). The extraction nozzle must be flush with the inner wall of the room and it should be installed near the door. The injection pipe should be installed in the middle of the wall and it should extend into the room for 30 cm minimum. Nozzles which are mounted in subterraneous cellar windows (light well) should be extended with a bend (no elbows) in order to have the coupling easily accessible,see pic. 4. Abb. 6: Nozzles for injection and extraction in a light well To fill a storage room with a silo truck the following requirements must be met: If possible the nozzles for injection and extraction should end out-of-doors. In either case an adequate distance for shunting must be planned for the coupling of pipes. Seite 9

10 The pipes should be as short as possible (less than 10 m) and be as straight as possible. If a straight pipe is not possible, only bends and no elbows should be used. If the nozzles are not out-of-doors and the pipes pass through other rooms, they have to be built according to TRVB H 118. The nozzles for injection and extraction must be made of metal, secure from turning out of position and earthed. The coupling of the injection nozzle must be a suction/pressure coupling for a tube with an inner diameterof d = 100 mm. The coupling for the extraction nozzle must have the same dimension or an inner diameter of d = 150 mm. After the filling the nozzles must be sealed with an adequate dummy coupling. Outside the storage room a socket with a mains voltage of 230 V and a fuse protection of 16 A should be accessible Access to the storage room An outward-opening door which meets fire resistance class T30 must be installed. On the inside a pressure relief should be mounted to guarantee access to the storage room at any time. If possible the door should be near the nozzles for injection. Thus the storage room is accessible for as long as possible because during the injection the pellets fall at the opposite side of the nozzle. The pressure relief of the door can be made of wood plates or with tongue and groove planks, which are put into profiles/sections. An optical level monitoring system (e.g. a window) is recommended but not obligatory. Abb. 7: Situation of a door into the storage room Seite 10

11 6.3.6 Buried tanks Buried tanks are often used if there isn t any space to install a storage room, for example when no cellar exists. They can be built in a garden or even under a car-park. The construction of these tanks is always made by a speciality firm. They handle the excavation, the insertion of the tank, the connection and the reconstitution during 1 or 2 working days. Concerning the tank- it s important that it has no joints. The tank as well as the tank cap must be made of weatherproof and corrosion-resistant material. In choosing the material it must be considered that it has to avoid the intrusion of humidity permanently. A buried tank must be equipped with a manhole including a walkable or drivable cover that prevents the intrusion of water. The connection between tank and the manhole must be waterproof. The tank cap must waterproof the tank andthe fittings on the cap must be sealable as well. An uncontrolled air exchange between tank and environment is not allowed. Abb. 8: Buried tank for the storage of pellets outside the building 1 subterranously installed pellet tank 2 manhole 3 manhole - covering 4 injection nozzle 5 suction lance for the extraction 6 Pellets pipe 7 conduit for return air 8 boiler with suction turbine 9 filling material For the connection between tank and central heating room a protective pipe has to be passed at a minimum depth of 300 mm. In that pipe the earthed pipes and other conduits must also be passed. The tank must be equipped with an adequate extraction system which allows the extraction of the pellets without problems with a sealed tank cap and with sealed fittings. The rest of pellets which can t be extracted must not exceed 5 % of the filling volume/nominal volume. Seite 11

12 6.3.7 Storage container Storage containers which can be erected in a cellar, in an adjoining building or in other unused rooms represent a cheap alternative to a classic storage room as described previously. Storage containers can - according to the structural determinations - be positioned directly in the central heating room as well. Different systems are available, the cheapest system is a tank made of fabric carried by a metal frame. Alternatively, tanks made of plastic or metal are also available. Pellets contain a certain fine fraction which gets dispersed, especially during the injection. This dispersed fine fraction can easily form an ignitable conglomeration, therefore ignition sources must be absolutely avoided. These include electrostatic charges. Metallic containers must be earthed and protected from corrosion. When using containers made from non-conductive materials all the conductive parts as well as all the fittings and the extraction system must be earthed. For flexible storage containers antistatic material has to be used. Concerning the installation of a flexible container it s important to have an adequate distance between wall and ceiling to guarantee the accessibility for maintenance and to avoid the damage of the fabric caused by rubbing against the wall. The nozzles for injection and extraction can be passed either through the exterior wall outwards. Or they can be mounted directly on the container, if an exit window, door or cellar well exists. Containers without an extraction nozzle (e.g. flexible storage container) need to be able to discharge transport air (e.g. an open window or door during the procedure of filling). To install the extractor fan outside a distance of 2.5 m between extraction nozzle of the container and an opening (e.g. window) should not be exceeded. (see pic. 10 and 11). Abb. 9: Example of the installation of a storage container with both nozzles inside the room Seite 12

13 Abb. 10: Example for the installation of a storage container with both nozzles outside the room Abb. 11: Example of a flexible container made of fabric Source: ÖkoFEN Pelletsheizung Seite 13