Which extraction system is most suitable for your situation depends on a number of factors, such as the capacity required, the number of machines to be connected and the frequency of use. For more information, see the dedicated page on our website.
Riedex extractors offer different ways of handling waste. The most common is the B-version. The B-version is equipped with one or more waste bins into which a plastic bag is placed. The plastic bag fills with waste and the level can be checked through a viewing window. Is the bag full? Then it can be tied up and disposed of with the residual waste. When disposing of the bags, remember to use an FFP2 mouth mask.
Another version is the so-called P version. This version is chosen when an extraction unit is placed on top of a briquetting press. The residual waste from the processing machines is processed directly into the press, compressing the waste with a ratio of about 8 to 1. This significantly reduces the disposal costs of the residual material or the residual waste can be used to feed a burner, for example.
The RV version that Riedex has in its range is the version with the rotary lock. The rotary lock is used for pressure-free dumping of material in, for example, container or silo. The extraction system is raised and a roller container, for example, can be placed under the rotary sluice. An RV version can also be constructed at ground level, with the bottom of the rotary sluice flush with the floor. In this way, the material can be further processed via a storey floor. Rotary sluice is also increasingly used when filling a briquette press, the advantage of which is that the briquette press is not sucked under pressure and the internal "dirty" air volume is also not too large so that the combustible volume is also reduced.Finally, Riedex supplies the C version which is used to fill 20-foot containers, for example. The C version consists of an RV version combined with, among other things, a transport fan with piping to fill an open or closed container. This version is mainly used for companies that process too much and/or too fast residual waste and where the other versions cannot keep up. The C-version can also be used, for instance, to circulate a material flow over a briquetting press by means of a cyclone with ring piping. The possibilities are endless.
Indoor installations are filters with a maximum capacity of 8000 m3/h and which are manufactured according to standard EN-16770. This is the applicable standard for indoor wood dust extraction, but the standard extends this to all suctioned or processed materials falling into Explosion Class St1. The minimum ignition energy of the material must not be lower than 10 mJ and/or have a lower explosive limit (LEL) than 30 grams per cubic metre of air.
The filters are characterised by a small internal "dirty" air volume. This is the amount of contaminated air that is inside the extractor before it is separated by the filters and could potentially cause danger through fire or a possible dust explosion.
Due to the small size of the filter and other mandatory items such as filter monitoring, pressure-resistant housing and minimum performance requirements regarding vacuum and volume, these filter units meet high safety requirements so that they are considered safe for use inside a workplace. After all, the risk of injury from fire or explosion is higher on the inside of a building than on the outside, as people are more likely to move past the filter.
Certainly an indoor set-up can stand outside, but with a few minor adjustments. We do recommend using a canopy, but it is not necessary. The unit is adapted to minimise possible weather influences and the discharge opening is also moved from the top to the side of the filter unit. It is possible to make use of an air return duct, to circulate the warm air from the workshop back inside as well.
In the Netherlands, we are mostly used to working with open containers. The designation "open" container indicates the use of a filter cloth with a cover to vent the container. This type of container can be filled with a transport fan. Besides the "open" containers common to us, "closed" containers are often used in the countries around us. These containers are made entirely of steel and not adapted with an openwork roof. With these containers, it is important to use a ring duct, which results in the transport fan circulating dusty air and therefore needs to be dust-tight. Other container couplings are also necessary. And whereas an open container can use a pressure gauge as a full indicator, a ring line requires a level switch.
Riedex extraction systems use different ways of switching on. The DM-120/160/200 are equipped as standard with an on/off switch on the front, combined with the possibility of switching with an external potential contact. In other words, it is possible to switch a machine tool along with the extraction.
This can be taken quite literally. Via a simple make contact (NO) on the machine tool, preferably on the relay of the drive motor, any machine can serve as a control for extraction. Most machine tools are prepared for this nowadays. Just pay attention to the frequency of switch-on. If this is done with a crosscut saw, there is a risk that the motor protection switch of the fan motor will switch itself off for safety reasons. This is because the motor gets too hot due to frequent switching.
Frequent switching on is common and can be solved in several ways. From DM-250 and up, the exhaust system is fitted with a follow-up timer as standard. This makes it possible to let the exhaust run for longer than the operating time of the machine tool. We use 5 minutes as standard. If the processing machine is used again within 5 minutes, the after-run timer resets and the cycle starts again. This avoids multiple switch-ons and is better for the system. Besides too many switch-ons, this also prevents excessive cleaning of the filter hoses (after switching off), which significantly reduces wear and tear on the cleaning motor and filter hoses.
From the DM-250 onwards, in addition to the on/off switch on the front and the potential-free contact, we also offer the possibility of starting the extractor by remote control. This way, one can start and stop the machine at the workbench. Multiple remote controls can also be supplied with this system, allowing the user to start the extraction system at multiple locations.
Another option is to use a current measurement relay, whether or not in combination with a slide control. This method is exclusively used in Germany. Here, current measurement coils are connected to the power supply of the machine tools in the workshop. Either at the machine tools or, for example, in the building's sub-distribution unit. When a coil detects a current draw from any machine tool, the current measurement relay will start the extraction system. Also, in case of a slide control, it will open the appropriate electro-pneumatic slide belonging to the machine tool. In this way, the user no longer needs to think about the extraction, it will operate fully automatically, including the lag timer. Also, when using slide control, the valve will remain open and only close after the fan has stopped. This is very important in today's extraction systems. The negative pressure that these systems can generate can lead to long-term damage if the ductwork is fully closed, and must be prevented. This is controlled automatically with a slide control system. The disadvantage of this system is the higher installation costs because electro-pneumatic slides have to be used and cables have to be pulled from all machines and slides to the controller.
Furthermore, it is possible to add different circuits to the system. Do you want to distribute the fans to different machines? It is possible by switching on only part of the fans. Or do you want to use capacity control using variable speed drives? Or are you thinking about level measurement in the unit or silo?
We and our dealers are ready to deliver a system that suits your needs.
The choice of an extractor with variable frequency drive with negative pressure measurement depends on really only one question, do I always need the maximum capacity of the extractor or does it vary?
Because if the capacity varies, then the use of an AC drive can save a lot of energy and thus costs, benefiting the climate and your wallet.
A capacity control ensures that the unit's negative pressure remains constant regardless of the requested flow rate. Are you using one machine tool? Then the system will adjust the fan speed downwards until the desired pressure and corresponding capacity is reached. If a colleague then uses a 2e machine tool started, then the fan speed will increase to again the set pressure and correct capacity.
It is precisely this reduction in speed that enables energy savings. With fans, the rule of thumb is that a reduction in speed by 10% yields a reduction in energy consumption of 30%, if the speed decreases by 20%, the energy cost is halved.
Besides energy savings, a number of other factors come into play. The ageing of the filter hoses will be slower because the maximum flow rate is not always used, so the filter load will be lower. You avoid the start-up surge associated with running a heavy electric motor under load, this is especially interesting when working in premises with a smaller voltage supply. Less maintenance is required because the structure is less heavily loaded, something that also benefits the service life. The inverter monitors the electric motor and itself and will raise the alarm earlier in case of irregularities before greater damage occurs. Finally, working conditions will also improve because noise at both the machines and the extraction will be reduced while the requested flow rate will always be correct.
In short, if you have a workshop where the flow rate fluctuates a lot, it becomes very interesting to choose this.
Atex 153 is a workplace guideline. It describes how a (wood processing) company should deal with the dangers of dust explosions in the workplace and classifies workplaces into hazard zones of increasing severity (so-called Atex zones). Atex 153 is included in the Occupational Health and Safety Act and therefore affects all companies that work with flammable materials, including the wood processing industry. This is because, as part of the RI & E, they have to take stock of whether there could be a risk of explosion anywhere in the company (click here for an explanation). If so, one has to deal with the formalities of Atex 153, such as drawing up an Explosion Safety Document. Various trade associations in the timber sector provide comprehensive and adequate information on this.
Atex 114 is a product directive. It sets requirements for equipment intended for use in explosive atmospheres, i.e. Atex zones. This involves products that are themselves sources of ignition, mostly electrical components. These have to be approved by an EU-designated body (Notified Body) and then receive an Atex certificate, which states in which danger zone the product can be used. If no Atex zones (according to Atex 153) are present in a company, no Atex equipment (according to Atex 114) is needed either. In other words, equipment, which is not in an Atex zone, does not fall under the scope of Atex 114.
Explosion protection of extraction equipment
Because, as here explained, no Atex zones are present in the average timber company, Atex 114 is useless in determining the explosion risk of extractors present there, whether indoors or outdoors. Simply put: you cannot get an Atex certificate from an extractor. The risk assessment of extraction equipment then poses a problem, because it is obvious that there is a risk of explosion. However, that hazard is not in the components used, but in the dust-filled interior of the device.
So how should the explosion risk of wood extractors be assessed? This question is particularly important in the case of indoor extraction units. Can a dust explosion occur in such an extraction unit, and if so, how can workplace safety be ensured? Explosion safety experts tend to classify the inside of the unit into Atex zones. This is allowed, but makes little sense, as no ignition sources are built into these internal Atex zones. Of course, this was taken into account in the design. Therefore, Atex 114 again offers no solution here.
In practice, a dust explosion inside the device will be the result of an internal fire, which in turn is the result of sucking up external sparks, e.g. from a cut nail, or a jammed sanding belt. (The energy of a spark by itself is insufficient to ignite a wood dust cloud, flames are needed for that.) It is technically impossible to prevent something like this from happening, so the extraction unit will have to be built in such a way that the consequences of both a fire and an explosion are manageable. How to do that, the Atex directives cannot help, but fortunately European standards are available to us in this respect.
For outdoor installation, there is the standard NEN-EN 12779. As there is no workplace outside, explosion protection requirements are mainly limited to preventing an explosion from entering the equipment. This includes explosion check valves, U-bend diversions with explosion relief and provisions for extinguishing a fire. After all, fire almost always precedes an explosion.
For indoor extraction, there is the standard NEN-EN 16770. This standard has only recently come into existence, since the beginning of 2019. Before the publication of this standard, explosion safety of indoor standing extraction was a grey area for a long time and that was the main reason for the many questions and ambiguities. But it is now finally clear what indoor extraction must comply with. At least for newly delivered devices, the standard does not cover extraction that had already been delivered before its publication.
Key requirements at a glance:
- The device must be completely closed and operate at negative pressure (open extractors, such as one-bag extractors with filter element may no longer be supplied)
- The dust-bearing part of the interior must be limited in volume. This can only be achieved by keeping the filter area as small as possible and - very importantly - taking the outside of the filter elements as the dust side.
- Pressure-resistant construction (200 millibars). Due to the limited size of the extractor, an explosive flame front cannot occur, but rather a violent combustion with a pressure that rises to a maximum of 200 millibars. The construction of the extractor must be designed and tested accordingly.
- A self-contained extinguishing system must be fitted from DM-250 onwards. Up to and including DM-200, this is not compulsory due to the low dust-containing volume of the smaller dust filters.
Air return ducts are used to return, or circulate, potentially warm purified air back to the workplace. This prevents a building from being depressurised when significant volumes are moved. It also conserves heat; air that is circulated does not need to be reheated.
However, there are some requirements for the installation of a return duct. Among other things, the air flow from the extraction unit must be deflected twice 90 degrees or once 180 degrees before entering the room and the first bend must be placed within 2 metres of the extraction unit. The bends must also be fitted with explosion panels. Furthermore, an extraction unit must be equipped with a so-called summer/winter valve where a choice can be made between circulating or discharging the purified air.
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