Scholarly article on topic 'Carbon dioxide removal and capture for landfill gas up-grading'

Carbon dioxide removal and capture for landfill gas up-grading Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Lidia Lombardia, Andrea Corti, Ennio Carnevale, Renato Baciocchi, Daniela Zingaretti

Abstract Within the frame of an EC financially supported project - LIFE05 ENV/IT/000874 GHERL (Greenhouse Effect Reduction from Landfill)–a pilot plant was set up in order to demonstrate the feasibility of applying chemical absorption to remove carbon dioxide from landfill gas. After proper upgrading - basically removal of carbon dioxide, hydrogen sulphide, ammonia and other trace gas compound–the gas might be fed into the distribution grid for natural gas or used as vehicle fuel, replacing a fossil fuel thus saving natural resources and carbon dioxide emissions. Several experiences in Europe have been carried out concerning the landfill gas - and biogas from anaerobic digestion - quality up-grading through CO2 removal, but in all of them carbon dioxide was vented to the atmosphere after separation, without any direct benefit in terms of greenhouse gases reduction. With respect to those previous experiences, in this work the attention was focused on CO2 removal from landfill gas with an effective capture process, capable of removing carbon dioxide from atmosphere, through a globally carbon negative process. In particular, processes capable of producing final solid products were investigated, with the aim of obtaining as output solid compounds which can be either used in the chemical industry or disposed off. The adopted absorption process is based on using aqueous solutions of potassium hydroxide, with the final aim of producing potassium carbonate. Potassium carbonate is a product which has several applications in the chemical industry if obtained with adequate quality. It can be sold as a pulverised solid, or in aqueous solution. Several tests were carried out at the pilot plant, which was located at a landfill site, in order to feed it with a fraction of the on-site collected landfill gas. The results of the experimental campaign are reported, explained and commented in the paper. Also a discussion on economic issues is presented.

Academic research paper on topic "Carbon dioxide removal and capture for landfill gas up-grading"

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Energy Procedía 44 (2I01_1) 465-4720

Energy Procedía

www.elsevier.com/locate/procedia

GHGT-15

Carbon Dioxide Removal and Capture for Landfill Gas Up-grading

Lidia Lombardia*, Andrea Cortib, Ennio Carnevalea, Renato Baciocchic, Daniela

Zingarettic

aDipartimento di Energetica - University of Florence. Via Santa Marta, 3 - 50139

Firenze. Italy

Dipartimento di Ingegneria dell'Informazione - University of Siena. Via Roma,56 -

56100 Siena. Italy

cDipartimento di Ingegneria Civile - University of Roma Tor Vergata. Via Politecnico,1

- 00133 Roma. Italy

Abstract

Within the frame of an EC financially supported project - LIFE05 ENV/IT/000874 GHERL (Greenhouse Effect Reduction from Landfill) - a pilot plant was set up in order to demonstrate the feasibility of applying chemical absorption to remove carbon dioxide from landfill gas. After proper upgrading - basically removal of carbon dioxide, hydrogen sulphide, ammonia and other trace gas compound - the gas might be fed into the distribution grid for natural gas or used as vehicle fuel, replacing a fossil fuel thus saving natural resources and carbon dioxide emissions.

Several experiences in Europe have been carried out concerning the landfill gas - and biogas from anaerobic digestion - quality up-grading through CO2 removal, but in all of them carbon dioxide was vented to the atmosphere after separation, without any direct benefit in terms of greenhouse gases reduction.

With respect to those previous experiences, in this work the attention was focused on CO2 removal from landfill gas with an effective capture process, capable of removing carbon dioxide from atmosphere, through a globally carbon negative process. In particular, processes capable of producing final solid products were investigated, with the aim of obtaining as output solid compounds which can be either used in the chemical industry or disposed off. The adopted absorption process is based on using aqueous solutions of potassium hydroxide, with the final aim of producing potassium carbonate. Potassium carbonate is a product which has several applications in the chemical industry

* Corresponding author. Tel.: +39-555-4796349; fax: +39-555-4796342. E-mail address: lidia.lombardi@unifi.it

doi:10.1016/j.egypro.2011.01.076

if obtained with adequate quality. It can be sold as a pulverised solid, or in aqueous solution.

Several tests were carried out at the pilot plant, which was located at a landfill site, in order to feed it with a fraction of the on-site collected landfill gas. The results of the experimental campaign are reported, explained and commented in the paper. Also a discussion on economic issues is presented.

© 2011 Published by Elsevier Ltd.

Keywords: CO2; capture; chemical absorption; landfill gas; up-grading

1. Introduction

Landfill gas (LFG) is generated through the anaerobic decomposition of organic waste present in municipal solid waste. Landfill design and operation contributes to the decomposition process. Generation starts shortly after a landfill begins receiving waste and can last for up to more than 30 years after the landfill closes. The average composition of this landfill gas is about 50% methane (CH4), 45% carbon dioxide (CO2), and 5% nitrogen (N2) and other gases [1]. There are also trace amounts of non-methane organic compounds (NMOC).

The EC strategy to reduce greenhouse effect (GHE) from LFG 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 requires the collection of LFG, 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 CH4 into CO2, 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.

An alternative way of exploiting the LFG is based on appropriate up-grading processes - basically removal of carbon dioxide, hydrogen sulphide, ammonia and other trace gas compound - in order to improve its quality and to obtain a gas composition very similar to commercial natural gas [2]. In this case the gas might be fed into the distribution grid for natural gas or used as vehicle fuel, replacing a fossil fuel thus saving natural resources and carbon dioxide emissions.

Several experiences in Europe have been carried out concerning the LFG - and biogas from anaerobic digestion - quality up-grading through CO2 removal, but in all of them carbon dioxide - which is of biogenic origin - was vented to the atmosphere after separation, without any direct effect in terms of greenhouse gases balance.

In this frame an alternative process to remove and capture CO2 from LFG - for its quality up-grading -was analysed during the development of an EC financially supported project - LIFE05 ENV/IT/000874 GHERL (Greenhouse Effect Reduction from Landfill). The aim of the GHERL project was to remove carbon dioxide from LFG in order to improve its quality and to obtain a gas composition very similar to commercial natural gas (www.gherl.it).

With respect to previously mentioned European experiences of LFG/biogas up-grading, in this work the attention was focused on CO2 removal from LFG with an effective capture process, capable of subtracting carbon dioxide from atmosphere, through a globally carbon negative process. In particular, processes capable of producing final solid products were investigated, with the aim of obtaining as output solid compounds which can be either used in the chemical industry or disposed off. The adopted absorption process is based on using aqueous solutions of potassium hydroxide, with the final aim of producing potassium carbonate. Potassium carbonate is a product which has several applications in the chemical industry if obtained with adequate quality. It can be sold as a pulverised solid, or in aqueous solution.

Since the CO2 contained in the LFG is of biogenic origin, its removal from LFG followed by sequestration can be considered as an effective way of removing carbon dioxide from atmosphere, through a globally carbon negative process.

2. Materials and methods

The selected absorption process was analysed by means of experimental tests on pilot plant.

The pilot plant was built at a landfill site in Tuscany (Italy), in order to feed it with a fraction of the on-site collected LFG. The core of the pilot plant (Figure 1) consists of a packed column filled with a laboratory packing, with a height of 0,990 m and diameter of 0,080 m.

In the column an aqueous solution of KOH reacts with the CO2 contained in the LFG, at atmospheric pressure. The absorption reaction between KOH and the CO2 produces an aqueous solution of K2CO3:

2 KOH + CO2 * K2CO3 + H2O (1)

In this reaction, a KOH excess leads to an increased production of potassium carbonate, while a CO2 excess leads to the following undesired chemical reaction:

K2CO3 + CO2 * 2 KHCO3 (2)

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.

Figure 1 Schematic and picture of the pilot plant.

2.1 Experimental phase

The experimental tests were performed from August 2007 to February 2008, after a start up phase. The tests were executed with a continuous monitoring on the main parameters of the reaction. The

monitored parameters were:

- inlet and outlet temperature of LFG: these parameters were measured by two thermocouples. These thermocouples were placed inside the pipes where the LFG flows into;

- inlet and outlet temperature of aqueous solution: these parameters were monitored by two thermocouples. These thermocouples were placed inside the tanks where the solution flows from/into;

- inlet and outlet volumetric composition of LFG: the inlet and outlet CH4, CO2 and O2 concentrations were measured by a gas analyzer.

These parameters were opportunely and continuously recorded and elaborated for estimating the CO2 removal efficiency and the influence of temperature on the chemical absorption reaction. Furthermore, the tests were performed with changing reaction parameters; the aim of the tests was also to determine the best operative conditions for removing the maximum amount of CO2.

The initial design conditions were [3]:

- LFG flow rate = 20 Nm3/h;

- flow rate of the KOH aqueous solution = 30 l/h;

- KOH mass concentration = 48%.

However, after the first tests, the operative conditions were modified for estimating the influence of the principal parameters on the chemical reaction. The main parameters were:

- LFG flow rate: the LFG flow rate was maintained around 20 Nm3/h, as initial design conditions indicated;

- flow rate of KOH aqueous solution: tests were performed with 30, 40, 50 and 60 l/h;

- KOH mass concentration: tests were carried out with 23, 28, 33, 38, 48 and 53% of KOH in the aqueous solution;

- inlet temperature of KOH aqueous solution: this parameter was kept approximately constant (40-45°C); after the first tests it was noticed that the inlet temperature of the KOH aqueous solution does not influence significantly the CO2 removal efficiency;

- inlet LFG temperature: this parameter is influenced by the atmospheric temperature; for preventing water condensation problems, the final pipe that conveys into the reactor was covered with heated cables, controlled with a thermostat. In this way it was possible to regulate the LFG inlet temperature: its value was about 15-20°C.

The experiments were performed using the following procedure [4]:

- each test was registered in a technical sheet. In this sheet the following parameters were annotated: date of the test; starting and ending time of the test, KOH aqueous solution flow rate, KOH mass concentrations, CO2, CH4 and O2 concentrations in the LFG, KOH aqueous solution and LFG temperature, pH of the outlet solution;

- samples of reaction products were stored and subsequently analyzed.

3. Results

The CO2 removal efficiency of each test is reported in Figure 2. Values of interest for the removal efficiency can be reached only working with high KOH concentration (48-53%) and high solution flow rate (50-60 litres/hour).

Figures 3 and 4 report the CO2 and CH4 volume concentration recorded during the experimental test at the respective conditions of KOH=53% Flow rate=60 l/h and KOH=53% Flow rate=50 l/h, which resulted the cases with highest removal efficiency. After an initial starting phase, the CH4 volumetric concentration significantly increased up to values between 85 and 97%, approaching the conventional natural gas quality.

Figure 2 CO2 removal efficiency vs. solution flow rate for different KOH concentration

tests.

KOH =53% - Solution = 60 l/h

10.53.31 11.00.56 1 1.02.24 11.03.50 11.05.17 1 1.06.43 1 1.08.10 11.09.36 11.11.02

-♦- CQ2in % -■- CH4in % — CQ2out % -»^-CH4out %

Figure 3 Volumetric composition of entering and exiting LFG for test KOH=53% and solution flow rate=60 l/h.

KOH =53% - Solution = 50 l/h

-*-C02in % -B-CH4in % —C02out % -*-CH4out %

Figure 4 Volumetric composition of entering and exiting LFG for test KOH=53% and solution flow rate=50 l/h.

4. Economic Evaluation

With respect to the described process a preliminary economic assessment was carried out, with the aim of estimating the specific removal cost for CO2. It was suddenly evident that the process can be sustainable from an economic point of view only if the produced K2CO3 can be sold [5]. With this aim, a first technical assessment of the process required to obtain solid K2CO3 was carried out, leading to a first sizing of a system composed by three process stages of water separation: evaporator, crystallizer and dryer. The heat requirement was estimated in the ratio of about 1 kWh of thermal energy (saturated steam at 3 bar) per 1 Nm3 of LFG entering in the CO2 capture process. Such required heat can be obtained from heat recovery from engines conventionally used in landfill, which are able to produce about 1 kWh of thermal energy (saturated steam at 3 bar) per 1 Nm3 of LFG burnt in the engine. This means that half of the overall produced LFG should be burnt in the engines, while the remaining part of landfill gas could be processed by the CO2 capture system.

Table 1 reports the considered assumptions and results for the economic evaluation, including investment cost (for the absorption system, the heat recovery from engines - assuming that the landfill is already equipped with engines for energy recovery - and for the solid separation system) and the operating costs, for different size of plants (700-4.200 Nm3/h). Additional assumptions for the economic evaluation are 6,5% interest rate and 10 years for the investment amortisation time; 8.000 operating hours per year; 0,09 €/kWh electricity cost; 975 €/t cost for KOH; 880 €/t price for selling K2CO3. This two values correspond to the worst cases since KOH cost should vary between 910-975 €/t and K2CO3 price should vary between 880-950 €/t.

According to the results in Table 1, the CO2 specific removal cost appears to be too high if compared with other methods for which cost estimates for large-scale, new installations range from 5 to 55 US $ per net tonne of CO2 captured from hydrogen and ammonia production or gas processing, from 15 to 75 US $/tCO2 captured from a coal or a gas-fired power plant [6].

Table 1_Assumptions and results of the economic evaluation.

LFG collected Nm3/h 1.400 2.800 5.600 8.400

LFG to up-grading Nm3/h 700 1.400 2.800 4.200

CO2 removed t/h 0,47 0,93 1,86 2,79

KOH supplied t/h 1,4 2,7 5,4 8,2

K2CO3 produced t/h 1,46 2,92 5,84 8,76

Power consumption kWh/h 174 349 698 1.046

Removal plant € 440.000 675.000 1.055.000 1.380.000

Heat recovery system € 230.000 350.000 550.000 715.000

Solid separation system € 1.215.000 1.860.000 2.900.000 3.800.000

Total investment € 1.885.000 2.885.000 4.505.000 5.895.000

Investment amortisation €/year 262.212 401.317 626.667 820.022

O&M costs €/year 94.250 144.250 225.250 294.750

Personnel costs €/year 50.000 50.000 50.000 50.000

Electricity costs €/year 125.280 251.280 502.560 753.120

KOH cost €/year 10.610.600 21.221.200 42.442.400 63.663.600

K2CO3 selling €/year 10.283.291 20.566.582 41.133.163 61.699.745

Balance €/year 859.052 1.501.465 2.713.713 3.881.747

Specific removal cost €/tCO2 231 201 182 174

As a matter of fact, the results strongly depends on the assumed prices for KOH and K2CO3. Let's keep constant the price of KOH at 975 €/t while varying the possible price at which K2CO3 can be sold. In this case the results are reported in Figure 5.

It is evident how at increasing K2CO3 selling price, the specific removal cost decreases (negative values for very high K2CO3 selling prices and large size plant mean a net income from the process). With reference to a plant size of 1.400 Nm3/h, the specific removal costs becomes close to literature values [6] if it is possible to sell the K2CO3 at least 920-930 €/t.

O £ £ V

u aj Q. !/> M

TOO 1.400 2.800 4200

Plant size [Nrn3ih]

—4-880 €/t K2C03 -■-890 €/t K2C03 900€/tK2C03 910€itK2C03 -a^92®€/tK2C03 -»-930 €lt K2C03 -I- 940 £/t K2C03 -950 Cit K2C03

Figure 5

CO2 specific removal cost dependence from the K2CO3 selling price.

5. Future development

As a matter of fact the compound adopted for the chemical absorption process, which is potassium hydroxide, is quite expensive. For this reason, a kind of chemical regeneration process of the load solution, based on accelerated carbonation of alkaline industrial residues, as air pollution control residues (APC), bottom ash or steel slag residues, was proposed and will be investigated within the frame of another LIFE project (LIFE08 ENV/IT/000429 "Up-grading of landfill gas for lowering CO2 emissions" acronym: UPGAS-LOWCO2). The basic idea lays in using the calcium content of such residues in order to regenerate the carbonate and bicarbonate ions - in which the absorbed CO2 is transformed - contained in the load solution. The final expected regeneration products should be the precipitated calcium carbonate (CaCO3) and the initial potassium hydroxide.

The UPGAS-LOWCO2 project started at the beginning of 2010. The available preliminary results are quite encouraging with respect to the possibility of effectively regenerating the load solution from the KOH absorption process, especially when APC are used.

6. Conclusions

Results from pilot plant experiments highlighted the viability of a carbon dioxide removal technique from landfill gas. The method employs an absorption column using a potassium hydroxide aqueous solution as input. The final products are an almost carbon dioxide-free landfill gas (very similar in composition to the natural gas), and an aqueous solution of potassium carbonate. From an economic point of view the process is sustainable only if the produced potassium carbonate can be sold, so the economic viability depends on the market conditions. However the carbon dioxide specific removal cost is quite high with respect to other carbon dioxide capture techniques and it becomes competitive only if potassium carbonate can be sold at medium-high prices for this product.

The possibility of introducing a regenerative step of the absorption load solution is under investigation, with the aim of reducing the operating costs, using for the regeneration process scraps and residues, containing calcium, which can be obtained at low or zero cost.

References

[1] US EPA. AP42 Emission Factors: Municipal Solid Waste Landfills. Technology Transfer Network, Clearinghouse for Inventories and Emission Factors; U.S. Environmental Protection Agency. (1998). Government Printing Office, Washington, DC.

[2] Persson M., Jonsson O. and Wellinger A. (2006). Biogas Upgrading to Vehicle Fuel Standards and Grid Injection. IEA Bioenergy

[3] Lombardi L., Carnevale E., Carpentieri M. and Corti A., Carbon dioxide capture from landfill gas. ISWA/NRVD World Congress 2007, Amsterdam, The Netherlands, 24-27 September.

[4] Carpentieri M., Lombardi L., Corti A., Cenni G., Burberi L., Carnevale E. (2008). Pilot plant for CO2 removal from landfill gas. SIDISA 2008 - Simposio Internazionale di Ingegneria Sanitaria Ambientale. Firenze (IT) 24-27 Giugno 2008.

[5] Lombardi L., Carnevale E., Corti A. (2008). Landfill gas quality up-grading through carbon dioxide capture: environmental and economic evaluations. 16th European Biomass Conference and Exhibition. Valencia (SP) 2-6 June 2008.

[6] IEA. Capture and Storage of CO2. (2007). From IEA Greenhouse Gas R&D Programme: http://www.ieagreen.org.uk/ccs.html (Feb. 15, 2007).