LIFE ENVIRONMENT PROJECT LIFE05-ENV/IT/000874 GreenHouse Effect Reduction from Landfill Dipartimento di Energetica "Sergio Stecco", Università degli Studi di Firenze Dipartimento di Scienze e Tecnologie Chimiche e dei Biosistemi, Università degli Studi di Siena Centro Servizi Ambiente Impianti S.p.A. Cornelissen Consulting Services B.V.
Summary Landfill gas is generated through the anaerobic decomposition of organic biodegradable waste present in municipal solid waste, that is mainly kitchen residues. The anaerobic decomposition is a natural biological process that takes place in oxygen absence and starts shortly after a landfill begins receiving waste and can last for up to more than fifty years after the landfill closes. The average composition in volume of this landfill gas is about half methane (CH 4 ) and half carbon dioxide (CO 2 ). The EC strategy to reduce greenhouse effect (GHE) from landfill gas emission consists of a progressive reduction of biodegradable municipal waste going to landfill in order to reduce the production of landfill gas, as stated in the European Directive 1999/31/EC. The same European Directive 1999/31/EC considers the collection of landfill gas, from landfill receiving biodegradable wastes, to use it to produce energy or, when this is not possible, to flare it. As a matter of fact, flaring allows at least the conversion of CH 4 into CO 2, and this practice reduces of about twenty times the potential GHE. When energy is produced, also the avoided emissions from conventional energy production should be subtracted from the overall greenhouse effect balance, reducing it further. However, the CO 2 present in the landfill gas is left unaltered by the subsequent combustion stage, being emitted to atmosphere and contributing to the overall greenhouse gases balance (even though we are dealing with biogenic origin emissions). The aims of the project was subtracting CO 2 emissions from the overall balance through CO 2 removal from landfill gas - with the objective of reducing the Greenhouse Effect contribution generated by landfills. The project wanted to demonstrate the suitability and sustainability of a specific CO 2 removal technique applied to landfill gas, and to disseminate the results in order to support the development of similar applications. 2
Techniques and results The CO 2 removal from gaseous streams can be complained through Carbon dioxide Capture and Storage (CCST), which is aimed to remove and store the CO 2 in order to prevent its emission into the atmosphere. CCST generally consists of three steps: capture, transportation and storage. While capture technologies for CO 2 from flue gas are commercially available (e.g. CO 2 absorption with amines aqueous solutions), the second and the latter stages (transportation and final storage) are by far less developed. In particular the storage deals with gaseous/liquid CO 2 streams and may not be technically and/or economically feasible in a short-term period. An alternative capture method consists in capturing CO 2 by means of processes capable of storing it in a solid product. This final product can be either environmental neutral (thus, can be safely disposed) or having a potential commercial interest (e.g. for the chemical industry). A final solid product in which CO 2 is stored allows disregarding the usual problems connected with the final storage of the gaseous/liquid captured CO 2, and thus can lead to a more feasible short/medium-term technology. Among the possible removal processes, aqueous absorption by potassium hydroxide (KOH) solutions was selected. As a matter of fact, CO 2 and KOH react forming potassium carbonate (K 2 CO 3 ), which is found dissolved in the absorption solution and can be recovered in solid form. Potassium carbonate is a product which has several applications in the chemical industry if obtained with adequate quality (e.g., crystal industry, special glass production, potassium salts, inks and pigments, detergents, food industry, waste gas treatment). It can be sold as a pulverized solid, or in aqueous solution. In order to demonstrate the feasibility of this removal technique a pilot plant was built at the Casa Rota landfill site in Terranuova Bracciolini (Arezzo, Italy), managed by one of the project s partners. The pilot 3
plant basically consists of a packed column where an aqueous solution of KOH come into contacts with the carbon dioxide contained in the landfill gas, which is directly supplied from the landfill (figure 1). The overall view of the pilot reactor is given in figure 2, together with the schematic of the plant. The pilot plant was designed to process about 26 Nm 3 /hour of landfill gas (consider that the landfill gas overall flow rate at Casa Rota is about 1.400 Nm 3 /hour). Figure 1 Column reactor and internal packing. Figure 2 Pilot plant schematic and overall view. Several tests at different conditions were carried out on the pilot plant, in particular the effects of changing the solution flow rate and its 4
composition were investigated. Figure 3 shows CO 2 removal efficiency versus solution flow rate, for different KOH concentration tests. High removal efficiency (83-97%) can be reached working at high solution flow rates (50-60 l/h) and high KOH concentrations (48-53% in mass). 100% 90% CO2 removal efficiency [%] 80% 70% 60% 50% 40% 30% 20% 10% 0% 20 30 40 50 60 70 Solution flow rate [litres/h] KOH=23% KOH=28% KOH=33% KOH=38% KOH=43% KOH=48% KOH=53% Figure 3 CO 2 removal efficiency vs. solution flow rate, for different KOH concentration. Environmental benefit According to the pilot plant results, CO 2 removal can reach 83-97%. It was evaluated how such a CO 2 removal from the landfill gas can reduce the overall Greenhouse Effect deriving from the landfill (figure 4), in comparison with the conventional situation in a landfill where the landfill gas is collected and combusted in engines with electric energy recovery (figure 5). Results, in reference to a Nm 3 of landfill gas produced by anaerobic decomposition, show that a reduction of 8-10% with respect to the conventional situation can be reached (table 1). Actually it is also important to remind that produced K 2 CO 3 recovering the CO 2 from landfill gas is not produced elsewhere. Normally K 2 CO 3 is produced especially by combustion of CH 4, since this gives a cheap, clean and reliable source of CO 2. Hence, considering a Life Cycle 5
Assessment approach, the environmental benefit is even higher, since by this process primary fuel is saved. Conventional process (landfill gas Proposed process (landfill gas collection, CO 2 collection and combustion in engines with energy recovery) removal, combustion in engines with energy recovery) Escaped 3,40 kgco 2 eq./nm 3 Escaped 3,40 kgco 2 eq./nm 3 Landfill gas combustion 1,06 kgco 2 eq./nm 3 Cleaned landfill gas combustion 0,66 kgco 2 eq./nm 3 in engines in engines Total 4,46 kgco 2 eq./nm 3 Total 4,06 kgco 2 eq./nm 3 Avoided for electricity production -0,68 kgco 2 eq./nm 3 electricity Avoided for production -0,68 kgco 2 eq./nm 3 TOTAL 3,78 kgco 2 eq./nm 3 TOTAL 3,38 kgco 2 eq./nm 3 Assumptions: 60% landfill gas collection efficiency; 88% removal efficiency; 35% energy conversion efficiency in engines; 0,551 kgco2/kwh specific emission for conventional electricity; reference to the operating conditions of the experimental test 50 l/h solution flow rate and 53% KOH mass concentration. Table 1 Comparison of GHE emissions in the conventional situation and in the proposed process. Economic evaluation On the basis of the experimental results a scaled up design of a plant for CO 2 removal from landfill gas was carried out, with reference to a landfill gas flow rate of about 1.400 Nm 3 /h (similar to Casa Rota landfill) equipped with engines for landfill gas energy recovery. Also, it was sized a plant for K 2 CO 3 recovery from load solution which need an input of thermal energy, which is assumed to be recovered from exhausts from engines. On this basis the total investment was calculated with reference to the process scheme of figure 4. Also the operational costs were evaluated (including KOH, electricity, maintenance, labour, amortisation, K 2 CO 3 selling). In this way it was evaluated a positive balance for the overall process. This means that selling K 2 CO 3 it is possible to cover the investment and operation expenses, also having positive profits. 6
CO 2 REMOVAL LFG TE EE K 2 CO 3 Figure 4 Schematic of the application of the proposed process. LFG EE Figure 5 Schematic of the conventional landfill gas recovery process. Similar results were obtained also in the case of smaller (700 Nm 3 /h) and larger installation (2.800 and 4.200 Nm 3 /h). Transferability The proposed process has not technical limitations for its replicability. As a matter of fact the application of the process does not require the development of devoted devices, since most of the required components chosen in the process design are fairly standard components. As there are no technical limitations to using this process on many locations, it is worthwhile to assess the potential for the whole of Europe. The orders of magnitude involved are given here, based on the following data: Casa Rota landfill represents roughly 1% of the yearly landfill in Italy Landfill in Italy represents 10% of the total in Europe (EU-15) 7
The potential in the 15 member states which the European Union had in 2004 is therefore roughly 1000 times the potential calculated for Casa Rota. This means: - reduction CO 2 -emission: 7 Mt/year - consumption of KOH: 27 Mt/year - production of K 2 CO 3 : 28 Mt/year This process can be used for any source of CO 2, like for example biogas from anaerobic digestion. But also the application to combustion exhausts should be sized and evaluated. It is, however, important to have available enough heat and some electricity. With the preliminary design of the proposed process on real scale it was proved the technical feasibility and hence the applicability and reproducibility of the process itself. The results of the investment and operating costs balance showed a net income, hence the process is feasible from the economic point of view. However, the profitability strongly depends on the price of KOH and K 2 CO 3. There are no fixed prices for these bulk chemicals, so it depends on the actual contracts whether or not the profitability can be realised. The present supply of and market for KOH and K 2 CO 3 must be investigated to be able to predict the development of prices, in particular when a large new stream is generated by CO 2 removal on a large scale. 8