Conditions for an economical production and use of alternative fuels
Abstract
Basically, the entire pre- and co-processing needs to be worked out carefully before alternative fuels can be used. It begins with the technical assessment of the pyroprocess in the cement plant, as well as the assessment of the waste sources and its composition from which the alternative fuel shall be obtained and the number of impurities to be disposed of safely.
Part of the preparatory work is also the pe-engineering, the forecast of qualities, and its assurance under the operational conditions. It is strongly discouraged to be persuaded to buy a system without these preliminary works. The individual requirements for each pyroprocess of cement production and the thermal potential in the waste composition determine the technical and financial expenditure for the conditioning plant and thus the profitability of such a project.
The economic viability of such a project is largely determined by the enforcement of legal requirements and a sound disposal fee on a proper calculation basis. It has to be noted that the contract periods are not determined by the purchaser of the alternative fuels (i.e. the cement plant), but by the reliable access to the waste, including its disposal fees. A cement plant is not interested in being supplied with poor AF qualities over long contract periods, but it is much more interested in a quality-oriented bonus-/malus system on which regular settlements can be made. The terms of these purchase agreements must be negotiated individually.
It is shown how such terms depend on the level of the disposal fee and at what point the purchase of fuels will switch to a sufficient gate fee for the cement work. Finally, it is shown how a contractual basis for supply and billing can be created.
1.?????Initial situation
As one of the most energy-intensive industries, the cement industry contributes approx. 6% to global CO2 emissions. This is on one hand due to the CO2-containing limestone in the raw material, which accounts for approx. 90% of the entire mass flow, and on the other hand the use of fossil fuels, which account for approx. 10% of the intake to the rotary kiln.
These fuels are used to decarbonize the raw meal and to form the minerals of the semi-product clinker. This burnt clinker shall be ground into a standardized cement using electricity and by additional gypsum, fly ash, slag, or other aggregates. Subsequently, packaged and shipped [9] to the ready-mix plant to produce concrete for the final customer.
The concrete is installed in the structure using electricity and remains there for several decades, during which CO2 re-carbonates by the binders’ surface, and until the structure will be demolished.
To minimize CO2 emissions down this chain, the cement industry has committed itself to reduce approximately 38% of its total emissions by 2050. The measures identified are based on the important pillars of
Co-processing is the generic term for the material and thermal use of suitable and pre-processed wastes, which are converted and quality-assured to alternative fuels and raw materials (AFR).
Starting from the quarry [1], calcareous sludges, e.g. from the de-carbonization of process water in power plants, siliceous forms of foundry sand, or aluminum-containing sludges from clay, these mineral wastes can be used as raw material substitutes.
This fine ground raw meal [2, 3] is fed to the calciner [4] at the entrance of the calciner [4] and is falling against the hot exhaust gas into the rotating kiln [5] at approx. 1000°C. Then the iron- and aluminum-containing components react to form a melt and provide calcium and silicon with the necessary matrix to form clinker minerals at a flame temperature of ~2.000°C.
After the clinker minerals have been formed, the clinker granules are abruptly cooled down [6] and stored in silos [7]. To obtain cement, the clinker will be ground with gypsum, e.g. from flue gas desulfurization, as well as fly ashes from power plants, blast furnace slag, or similar, to produce standardized cement in the mill [8].
The highest production costs are nearly 30 % and are fuel costs, so cost-efficient alternatives have always been sought and with them the waste management industry and its ability to provide cost-efficient alternative fuels.
In Europe, the use of waste-derived alternative fuels started in the 1970th with used oil and is today subject to a huge range of waste sources and the corresponding directives. From a legal point of view, co-processing in a clinker burning process is strongly focused on the restrictive requirements of air pollution control. A basic requirement for reasonable use is therefore the maintenance of a temperature of at least 850°C for more than 2 seconds. Following these requirements, in general, there are several entrance points available to feed the kiln process best.
Most often, the calciner is used for feeding the low-grade RDF, which is simply prepared and of poor quality. However, setting up this feed point nevertheless requires a sound preparatory work to evaluate the bottlenecks and possibilities in the entire process and respectively in the calciner in terms of e.g. temperature profile, oxygen supply, mixing, residence time, and its burnout behavior or with the view to pre-processing to the particle size. The investment is enormous and the construction, as well as the preliminary work, should therefore be well prepared.
High-grade SRF is easier to feed via a satellite burner or sinter zone burner at the end of the kiln. However, this requires a higher degree of pre-treatment and a calorific value similar to lignite and does not tolerate 3D particles, which even affects the clinker quality by reductive burning conditions.
In the latest years, precombustion chambers are designed to be fed with a so-called high calorific fraction (HCF) in a grainsize of roughly 300 mm. These materials are difficult to process or to burn, such as windmill blades, sticky tar, resin, or coarse wooden biomass.
2.?????Definitions
Many different definitions, fancy names, or careless statements confuse or even lead to public and political rejection. Therefore, it is essential to use the right terms in the right context.
This implies not simply referring to waste, but dubbing them as waste-derived or better as an alternative fuel. This has nothing to do with concealment but is because enormous investments are made beforehand to convert waste into a specified and quality assured fuel that has to meet the requirements of a thermal production process. If this attitude is not in place from the beginning, the use of waste becomes a kind of waste disposal and the pyro-process will not accept alternative fuels after a certain thermal substitution rate (TSR).
Concerning the envisaged valorization process, several qualities shall the derived from waste. For the process of clinker burning and production of electricity there are several terms and specifications:
HCF – High Calorific Fraction, which is the combustible fraction with a higher calorific value than untreated MSW. After sorting out materials for recycling and segregating unsuitable impurities and water-containing organics, the grain size is <300 mm and its cv will range up to 15 MJ/kg.
It is the feedstock for a Waste-to-Energy plant (WtE) to produce process steam and electrical power. Or it will directly be used in a so-called pre-combustion chamber, which is linked to the calciner at the rotary kiln, or shall furtherly be blended and processed to
RDF – Residue Derived Fuel. This low-grade fuel, RDF suits best directly for the calciner to decarbonize the lime-containing raw meal at a long retention time (>5s). It’s mainly processed on the second step out of HCF, and in grain size between 60-120mm, and a cv ~13-19 MJ/kg.
SRF – Solid Recovered Fuel can simply be processed from purely collected industrial and commercial waste or -with a little more effort of cleaning and blending- from RDF. It is free of 3D particles and is processed to get the shortest retention time in the burner flame. Due to its proportions of waste-derived compounds, its cv can range similar to lignite (22±2 MJ/kg) or much higher.
3.?????Minimum requirements
Definitions and other issues are one part of the entire process that needs to be worked out carefully before alternative fuels can be used.
It begins with the basic technical determination of the pyroprocess in the cement plant, as well as the determination of the waste composition from which the alternative fuel is obtained and the number of impurities to be disposed of safely. Part of the preparatory work is also the knowledge of the mechanics and physics behind, the quality assurance up to the right feeding or operational issues. It is strongly discouraged to be persuaded to buy a system without these sound preliminary works.
The individual requirements for the pyroprocess of cement production and the thermal potential in the waste composition determine the expenditure for the conditioning plant and thus the profitability of such a project. Profitability is determined by several factors, which will be discussed in more detail below.
4.?????Economical frame
The decarbonization of limestone to produce cement clinker and the CO2 allowances are the two cost drivers and the main reasons for using alternative fuels and raw materials. Depending on the technology the clinker burning process varies from ~6 kJ/kgclinker (wet process) to ~3 kJ/kgclinker (dry process).
Since the first oil price ?shock“ in 1979 the cement industry started to seek cheaper energy and switched from oil to lignite, which also marks the specification of properly conditioned waste-derived AFs, today. The largest benefit of AF is by saving primary energy costs, which are accounting around 26% of the manufacturing costs. In addition to modernizing the plant equipment by using highly efficient technologies (e.g. cooler), the use of CO2-neutral fuels offers a quick option to save costs, as well. Consequently dry and preprocessed wood, paper, natural rubber, textiles, etc. are most of the interest concerning their neutrality, but its generated fuels must match mandatorily the energy demand of the thermal process.
About financing the entire waste management in many countries, the authorities levy the disposal fee by a certain percentage of consumption e.g. water, gas, or estate taxes, and transfer the responsibility inclusive of the budget to private companies. Although this financial budget is partly insufficient to cover all costs, the risk of corruption vulnerability is high due to the lack of legal enforcement and strict control.
E.g. in Europe, the disposal service is awarded by tender to obligatory state-certified companies, which are politically controlled and based on legal regulations. The waste disposal fee shall follow the polluter-pays principle, which has at least two main functions: first, to cover all the costs of reliable and legally compliant waste disposal, and second, to encourage people to reduce the amount of waste they produce by saving their own money.
In this case, waste cannot be avoided on all subjects of collection, transport, stuff management, sorting, conditioning, and recycling until quality monitoring, thermal use, waste incineration, or sanitary landfilling are subsumed in this disposal fee.
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To obtain reliable figures, the current situation is reviewed every five years as part of a waste management plan. This includes determining the number of inhabitants, the amount of waste per capita, or the composition of the waste.
So, the waste producer is the responsible owner and has to cover all the costs. The fees are directly linked to each collection and bin, which means you pay depending on the legal requirements and annual needs.
In the following, different scenarios are used to show which economic opportunities and possibilities exist to lead a project to success. The general conditions shall be assumed as follows:
On the side of the waste management industry:
On the side of the exploiting cement plant are exemplarily taken into account:
All costs are calculated per ton.
In the first case, which is the current starting situation in most cases, the polluter-pays-principle does not apply, i.e. the disposal fee remains at its known low level. A simple MBT technology is installed which will produce a low-grade fuel (RDF) with high moisture content and a low level of calorific value, but a high content of biomass.
To establish a reliable waste management system, the cement plant is willing to subsidize the system by purchasing RDF, even though its quality is at the lowest tolerable level.
By a quick review of the calculations, this project to produce alternative fuels in a simple MBT will fail, even despite financial support from the cement plant.
The damage caused by the introduction of moisture into the thermal process by the poorly treated RDF and the initial costs cannot be compensated by the savings in avoidance of fossil fuel and its reduction in GHG allowances. The financial loss is about 9 times higher on the plant side than on the conditioner side.
At this point, it must be clearly stated that the economic viability of such a project depends essentially on the enforcement of the legal framework and the certainty of the disposal fees, which must cover all the costs of a reliable and integrated waste management system that includes collection, sorting and conditioning up to the long-term operation of a sanitary landfill.
Under the existing contractual conditions and further subsidization by the cement plant, the MBT will be upgraded to produce a more suitable RDF for the calciner.
On one hand, upgrading the MBT will generate a better RDF quality with a higher biomass content and a lesser introduction of moisture, and consequently a higher thermal substitution rate at the cement plant. Its losses will be halved but will remain negative.
On the other hand, the costs in the MBT will rise to six times than before reconstruction and will bring it to its knees.
This means that the disposal fees have to be raised - significantly!
In addition, in this theoretical example, the cement plant shall waive a gate fee and on subsidizing the costs of the MBT to bring the calculation into a balance for both sides.
Nevertheless, the resulting financial cushion will be too tight for both partners to cover even the smallest expenses such as additional repairs or investments for a sufficiently equipped laboratory or the operation of a sanitary landfill. Finally, an MBT is a splitting plant, from which several streams are left to recycle, compost, and customize alternative fuels. But, also non-recyclables and impurities have to be disposed of safely in a sanitary landfill or even incinerator. These investments have to be covered by the polluter-pays-principle, as well.
In this last example, the polluter-pays principle is valid, and the appropriate disposal fee will cover all the investment into a suitable technology to produce RDF with a suitable quality. The cement plant will extend its reception and storage facility to guarantee a continuous supply and will get a gate fee to compensate for its higher investments such as SCR- or SNCR-technology to reduce NOx emissions.
Finally, an additional WtE-plant to produce power may complete this system to ensure public and private cooperation for an integrative, safe, and reliable waste management.
5.?????How to draw up a supply contract
As already mentioned, the contract periods are not determined by the cement plant, but by the reliable access to the waste, including its disposal fees. A cement plant is not interested in being supplied with poor AF qualities over a long contract period, but rather in qualities and on-demand.
Later, when the MBT is in operation and the cement plant is continuously supplied, these qualities must meet the agreed specification of the clinker production process and will also be the basis for its frequent billing. The terms of these purchase contracts are usually negotiated individually and monitored by regular inspections at the reception on the cement plant side. Incidentally, this billing model can be extended or shortened as desired according to the agreed bonus/malus system.
This also shows very clearly that it is always worthwhile to assess the composition and properties of the intended input waste in detail in advance and to design the processing plant accordingly, which has a huge impact on the investment, to produce customized RDF qualities for the calciner or SRF for the main burner.
Quality assurance according to defined standards will provide the required parameters for cross-checking. For this purpose, the statistical median and the 80th percentile have proven to be useful by means in which both sides can bill in a certain rhythm.
The following shows when several parameters have been agreed upon, which are analyzed regularly during the delivery period. Finally, these are set in advance as the settlement basis and tolerance, so that a settlement is based on these results or their deviation.
In the following example, four typical parameters (calorific value, and the content of chlorine, moisture, and biomass) are identified by this individual cement plant. This billing basis can be extended or shortened as desired for individual supply contracts.
Here Example 1 shows the consequences if the promised specification is not met. However, Example 2 also shows how much profit can be made if the system is designed and operated, properly.
And, this also shows very clearly that it is always worthwhile to assess the waste composition and its properties precisely beforehand and to design the processing plant to this, i.e. to invest to produce tailor-made qualities and to ensure their quality and continuous supply.
The entire system only works in a sustainable manner and for the benefit of society if both sides are aware of the context and consequences.
More detailed contract templates can be found on https://wltp.eu/activities/ and in the appendix of the WLTP Directional Compass: Alternative Fuels Handbook for Project Managers
Contact
WhiteLabel-TandemProjects e.U.
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Managing Director bei aixprocess GmbH
2 年Hubert, thank you so much for posting these important aspects that are obviously often negelected when using AF in cement plants. We are more often engaged to trouble-shoot the process and quality issues coming from inappropriate AFs (or better their inappropriate use) than to predict the behaviour of certain AFs in specific kiln lines. It should be the other way round.
Better thinking 14 days ahead, than to reconstruct a life long!
2 年Hubert Baier