Analytische NIR - Technologie
Specialist article: Substitute Fuel Sorting with NIR Technology 30.07.2006
Specialist article
Quantum Leap in Sorting Analysis
Processing High-Quality Derived Fuels
Rubbish sites for untreated waste have been closed in Germany since the middle of 2005. This was a nightmare for many medium-sized waste disposal companies. Since that time there has not only been a shortage of combustion units, but disposal prices have also risen in some regions by up to 300% ad hoc.
So what should be done with residual waste? (Figure 1). The call for sensible recycling paths for sorted residue and residual waste took on a whole new dimension overnight. One interesting solution involves replacing primary energy sources like coal, gas and oil, which are becoming increasingly scarce and more expensive, with what are known as substitute fuels for energy intensive sectors like cement works and power stations or furnaces or other large industrial combustion plant. The market for substitute fuels is currently developing into a major player in the energy mix.
Figure 1 (Bild1_RDF_mat)
But two criteria have to be met if substitute fuels are going to be used at all as fuels with a constant fuel quality in the sectors mentioned above:
- a consistent calorific value
- a consistent ash content level.
Both science and industry have been trying to further develop individual process stages for processing waste technically to turn it into substitute fuels with the aim of guaranteeing consistently good calorific values to achieve some degree of quality assurance and performance that matches the classical primary energy sources.
One particular challenge involves removing contaminants from the substitute fuel in an efficient manner – e.g. parts containing chlorine in the form of PVC plastics.
Sorting Waste
In order to exploit the energy potential in waste on an industrial scale, a mechanical process is urgently required. The separated mixed waste originating from domestic, bulk and commercial waste and mixed plastics from the recycling scheme can then be available for use in generating energy. The waste is normally undergoes the following processing stages:
1feeding and continuous dosage of waste,
2preliminary crushing of large elements,
3 segregation of metals,
4 air separation or ballistic separation of paper and foil,
5segregation of plastics and other combustible materials,
6further crushing,
7compacting of the fuels or processing them to what is known as fluff.
To ensure that these processing stages are carried out at the sorting centres in an efficient manner in order to guarantee clear separation, optical near infrared (NIR) sorting machines are used, amongst other things. All these kinds of optical sorting tools are surface-scanning systems and they measure the side of the object that is turned towards the sensor.
Standard Sorting Tools
Substitute fuel negative sorting with NIR sorting tools involves deliberately identifying and removing contaminants (e.g. PVC) from the material flow of pre-treated substitute fuel feed (Figure 2). The integrated NIR sensor recognises the contaminant using detector belts, which are arranged over the complete sorting width and then issue a command to discharge the item using compressed air.
In what is known as substitute fuel positive sorting, plastics, e.g. PP, PS, PE, paper and cardboard can be deliberately removed to ensure that the substitute fuel that is obtained is exactly defined. The PVC parts containing chlorine pass through the sorting machine in the positive sorting mode.
(wlb_EB_pos_neg+PX.ppt)
Figure 2: Positive or negative sorting in the standard version
Sorting Tools with a Double Discharge Facility
In the PX technology developed by RTT involving two discharge belts for processing substitute fuels, it is not only possible to remove contaminants from the feed material, but also create a new fraction, e.g. PET. This sorting tool can fulfil the function of two standard sorting machines (Figure 3). As a result of its second discharge nozzle, it is able to provide a three-fold separation of the flow of materials into two sorted fractions and one fraction passing through in one sorting procedure.
The machine can be operated both in the negative and positive modes at the same time. On the PX machine, the materials being sorted are fed on to an accelerated conveyor belt as in the standard version of an NIR sorting machine. Using analytic NIR technology, the sensor detects all the items on the belt and, depending on their chemical composition and classification, allocates them to one of the intended fractions, the first or the second nozzle or the residual mass remaining in the machine. The discharge nozzles can be allocated to match the feed material and can be freely programmed.
There is also another advantage: both of the substitute fuel fractions, from which contaminants have been removed, can be mixed with each other in such a way that a constant derived fuel is created at the end of the process with an adjustable calorific value and a defined ash content.
The substitute fractions individually produced using this process can be marketed much easier as a single fraction.
(wlb_EB_pos_neg+PX.ppt)
Figure 3: positive and negative sorting in one stage
Description of the Way the PX Option Works
The requirements for sorting bulky waste are different from sorting domestic waste. When feeding in bulky waste, most of which is made of wood, outlet no. 1 is used to remove any PVC from the feed material. Outlet no. 2 removes defined plastics. The wood fraction is the fraction that passes through the machine. Two different qualities of substitute fuel are created in one sorting stage (no. 1 and no. 2 substitute fuels). The no. 1 substitute fuel contains selected plastics and has an extremely high calorific value and a low ash content. The no. 2 substitute fuel mainly consists of wood. The wood fraction has a slightly lower calorific value and a relatively high ash content.
When feeding other substances into the sorting machine, such as mixed plastics waste, the plastics pass through the machine and produce a no. 1 substitute fuel. Outlet no. 2 on the machine can produce a paper, cardboard and paperboard fraction and therefore provides a no. 2 substitute fuel. Outlet no. 1 gets rid of the contaminating PVC parts.
New Analytic NIR Technology
The development of the 64 Multiplex technology marked a minor quantum leap in analytical NIR spectroscopy. This further development is technologically superior to the old NIR standard techniques in that it can handle extremely large amounts of measuring data. More than 5,800 measuring blocks are measured per second using the Multiplex technology with its 64 measuring heads; two times 128 (256) discrete wave lengths are recorded, summarized and analysed by each measuring block This involves more than 1.5 million items of data that are measured, all of them with an information content of 16 bits. The scanning process carried out by the 64 measuring heads takes place in less than 20 ms. Assuming that the belt travels at approx. 2.8 m/s, the flow of materials on the belt is measured and sorted without any interruption. As a result of this innovative technology, the sensor is able to handle and detect fraction sizes from 10 mm upwards or it can cope with sorting widths of up to 4 meters on an accelerated conveyor belt.
(Bild 05_NIR_operation)
Figure 4: NIR sorter
(Bild 06_NIR_sortierer)
Figure 5: NIR sorter
The new NIR sensor has been especially configured for sorting substitute fuels and its wave length and spectral reflection are exactly calibrated internally during each measurement run. This is an absolute precondition for any precise, analytical assessment of the objects being measured. Following the recognition and sorting process, the measuring data on the detected parts are then overwritten by subsequent data, as no use for the old measuring data has yet been discovered.
Substitute Fuel Quality Management – Statistical Data Gathering
The individual measuring data are currently being gathered and recorded in an R&D project involving the Zittau/Görlitz University of Applied Sciences and the Amand corporation in Dresden. The aim of this project is to develop a complex data base, which will allow statistical inferences to be made on the material parameters of the goods being sorted.
Substitute fuel quality parameters, for example:
•moisture content
•PVC contamination
•composition of materials in percentages
•calorific value
•degree of utilisation of the sorting machine
The measuring data are being continually gathered, processed statistically and documented. Once they have been processed, these material parameters can be utilised by operators for quality assurance purposes.
Existing sorting machines can also benefit from this comprehensive measuring data expertise contained in this data base by being upgraded. This marks a further indispensable milestone towards producing substitute fuels with a quality seal.
Author:Ernie Beker,
Authorised signatory
RTT Systemtechnik GmbH, Zittau
E-mail Home page:
Figure 2:
Material feed
Sensor
Conveyor belt
Compressed air outlet
Standard option (positive or negative sorting)
Negative sorting
Positive sorting
Passing through
Discharge
Substitute fuel
Figure 3:
Feed
Sensor
Unisort PX Triple Principle
Substitute fuel processing
Discharge belts (freely programmable)
Feed (pre-treated)
Passing through
Outlet 1 e.g.
Outlet 2 e.g.
A. Bulky waste (mainly wood etc)
Wood etc / substitute fuel 2
Substitute fuel 1 suitable for use as fuel etc
Parts containing chlorine, other contaminants
B. Mainly plastics (mixed plastics from recycling scheme)
Plastics. substitute fuel 1
PP, compounds etc, substitute fuel 2
Parts containing chlorine, other contaminants
C. Domestic and organic waste
Residual waste
PP, compounds, etc, substitute fuel 2
Selected plastics, substitute fuel 1
Author: Ernie Beker, RTT Systemtechnik GmbH, ZittauPage 1 of 6