SRF Goes Green in Portugal

The organic fraction is dried to a moisture content of less than 20%, at which point the green SRF has a calorific value comparable to many forms of biomass A waste treatment system which obtains a new product, dubbed 'green SRF' from the organic fraction of waste has been developed at a recycling facility in Portugal. Due to its composition, combustion analyses and calorific value, the product has already been awarded biomass status in several countries. By Patricia Masias Are environmental sustainability and the improvement of profit ratios compatible? In the case of waste treatment, it is fair to say that these twin goals are not only compatible but that their coexistence is a necessity. In an effort to reconcile these two often competing goals, Masias Recycling recently set about developing a system that could help close the circle of recycling and recovery for input materials at material recycling facilities. Further, the aim was to maximise the closure of this circle within a single facility, thus reducing the facility's dependence on third parties. The result of this development is a system that is capable of producing a new combustible product from the organic fraction of waste - green SRF®. At present, waste is often an untapped raw material. For this reason it is necessary to innovate, and innovating in this industry means exploiting all recoverable waste to the full. To close the waste cycle it is important to combine concepts such as 'operating profit' and 'efficiency' in economic terms. The optimisation and full exploitation of available resources, along with appropriate organisational decision-making, is the gateway to an improvement in efficiency, and as a consequence to an increase in the operating profit of a plant. The green SRF concept is the result of introducing new elements, not at specific points in the process, but rather to the waste treatment concept itself. Sustainability and profitability These are difficult economic times and new paradigms must take full account of the need to grow profitability, but also increase sustainability. This change mainly manifests itself in two directions: on one hand, a renewed concern for the sustainability of the industrial processes; and on the other, a need to make this social and environmental awareness compatible with financial profitability. For the development of new solutions, it is essential to question the parameters we know, and within the waste treatment scenario, to therefore ask ourselves a question: why not classify waste, as we should, by its nature and not just by its origin? The aim of this question is to express that it would be logical to classify waste by the materials of which it is composed and not by its origin. This is because a material can have different properties even if it comes from the same place, and this material may be similar to another from a different place. In order to generate the minimum reject fraction in a recycling plant, the activity of any treatment begins with the input of the material. From there, a series of mechanisms and processes come into play to recover the maximum possible percentage of recoverable products. However, in terms of operating profit, in a classic MSW plant, the reject fraction is high and the profitability is too low. To illustrate this, we can take as an example a plant which treats 100 tonnes - a rounded figure - and from this point on, we can see how the operating account improves as the waste treatment system is modified. Scenario One - The Classic Model In figure 1 we see a classic MSW treatment plant where we start with mechanical separation using screening trommels, bag opening, organic fraction recovery using another screening trommel, and recuperation of the recoverable materials of the excess of the trommel by means of a ballistic separator and an optical separation system. The most important data we can extract from the diagram of this so-called classic plant are that in this model there is a 49.5% reject fraction, 6.77% recoverable materials and 12.23% is compost. Figure 1 Analysing the operating account of a plant of this type, for 100 theoretical tonnes of waste, the operating account has costs arising from the pre-treatment, production and transport of compost, and from landfill costs. On the other hand, it receives revenue from the gate fee for waste, from the recuperated recoverables and from the sale of the compost. All of these elements mean that the balance of the operating account of a plant of these characteristics has a final profit of around. 5% Scenario two - MSW AND SRF TREATMENT PLANT In a second model, we review the difference to the operating account of the plant when an SRF production plant is added to the end of the MSW treatment line. In this scenario the quantity of waste going to landfill is reduced by approximately 50% as compared to a classic plant, and a new product appears, considered to be a marketable high-quality SRF. The operating account records new revenue derived from the sale of high-quality SRF and also, by reducing the percentage of reject fraction going to landfill, gates fees are also reduced. This makes the operating account vary until it arrives at a final profit of approximately 15%, counting the sale of the SRF. Scenario three - MSW + SRF + GREEN SRF At this point, we focus on modifying the SRF treatment line. The compost production is annulled and replaced by the production of an additional, lower quality, SRF. This is formed from the organic matter contained in the waste, which is dried and known as green SRF®. At this point, the setup of the plant changes completely and now features the following machines: a feed with a trommel to remove the bulky materials, the trommel excess goes to a biodrum where the humidity of the material is reduced, it is homogenised, the cellulose is defibred and partially decomposes. It must be emphasised that all the paper (cellulose) is integrated into the organic matter (residence time of 36-72 hours). The material then enters a trommel to separate the fraction greater than 40mm, which is sent to mechanical separation (free of paper) to recuperate the recoverable materials - materials are also recovered to produce a high-quality SRF. The fraction under 40mm (remember that it is the organic matter + the cellulose) passes through a metals recovery process and is then put into a continuous drier to reduce the humidity of the mixture to below 20% and increase the calorific value. The material obtained when the drying process is complete is the green SRF product. If the operating account of this model is examined, greatly reduced landfill costs can be seen, as only 4% of materials enter the reject fraction, and there are also additional revenues generated by the sale of the green SRF. It should be added that in this case, all the costs of the compost production process are saved - which in many cases is a deficit. This means that the final operating profit of the plant is approximately 40%. MSW + SRF + GREEN SRF + BIOMASS BOILER What is biomass? The Spanish Royal Academy dictionary defines biomass as the biological resources of vegetable or animal origin, including the materials resulting from their transformation, from which an energy fuel can be obtained, whether directly or indirectly. This definition is completely applicable to green SRF, considering them as a same type of product. The tests prepared for green SRF also reveal high LCV figures, even in acceptable humidity conditions. In this new scenario green SRF provides as much or more calorific value (LCV) as traditional biomass, thus making it a very interesting energy source. This is why we are making great efforts to convince the public administrations to consider this type of green SRF material as a biomass. In Portugal, where the first such plant has been developed with waste and recycling company, Resitejo, this is already the case. The Portuguese example As can be seen in figure 2, the plant is arranged the same as in scenario three, with the difference that in the very near future the dried green SRF leaving the dryer will be put into a biomass boiler which will generate marketable electricity, as well as enough heat to supply the dryer. Figure 2 This means that there will be no need for any external energy source to dry the green SRF, as the biomass boiler will generate enough energy for this purpose, as well as a surplus which can be used to generate electricity. The ashes which are remain after combustion will be considered as a reject fraction. If the operating account of a plant of this type is analysed, it can be seen that all of the energy supplied to the dryer is saved. However, it is also important to consider the capital and operating costs of the boiler, while at the same time counting the revenue received from the sale of electricity. This revenue has been considered with no subsidy on its sale price. In this scenario, and considering that as with Portugal, the green SRF is considered as biomass, the profit of a plant of this type rises to approximately 60%. Green SRF and cement Kilns After all of these scenarios for which we have extracted estimates of operating profits with real bases, the potential use of green SRF in cement plants is also worth considering. Despite their usefulness, cement plants are burdened with a negative image with regards to sustainability, and are often considered 'dirty' in the urban landscape. Cement plants are also responsible for nearly 5% of mankind's CO2 emissions globally. However, it should be emphasised that the use of biomass in cement plants around the world has risen from 300,000 tonnes in 1990 to 4.9 million tonnes in 2009. In fact, it is calculated that the use of alternative fuels in cement plants will grow more than significantly in the coming years. In 2012, it was calculated that the percentage of energy replacement used in these types of plant by alternative fuels ranged between 5% and 10%. While the forecast for the year 2050 is 37%. Therefore, indirectly it could be considered that there is another large market for green SRF. Conclusions The technology has already been designed, produced and assembled in the Portuguese plant of Resitejo. Despite the fact that this is the first step in implementing the concept, it is the result of a lot of work and is the fulfilment of a challenge to close the circle of waste. The road to imagining and making this plant a reality gives us the chance to become benchmarks when planning and sharing this model, which can provide benefits, not only for the Environment, but also for its operators. Patricia Masias is area manager for Masias Recycling