Landfill gas to electricity project

L.J. STRACHAN - Project Manager, Department of Cleansing and Solid Waste (DSW), eThekwini Municipality (formerly Durban Metropolitan City Council), Durban, South Africa (RSA); B. COUTH - Technical Director, Consultant, Enviros, Shrewsbury, UK; R CHRONOWSKI -  Senior Environmental Specialist and Project Development Specialist, Africa Region, PCF (Prototype Carbon Fund), The World Bank, Washington, USA.

Summary

A project currently being developed by the eThekwini Municipality aims to address global warming and climate change, the most serious environmental issue facing the world today. Africa is already suffering significant effects of global warming.

The eThekwini Municipality proposes to enter into a project, a first for Africa, that will highlight the successes of the World Summit on Sustainable Development (WSSD, Johannesburg, 2002). The project aims to utilise landfill gas from three municipal sites to yield annual 10MW of power.

This paper initially describes the three project sites, the gas modelling and yield predictions, and utilisation technologies and options.  It then goes on to describe in further detail the Climate Change Mechanism (CDM) and the financial viability of the eThekwini Municipality project.

1.  Introduction

Global warming with climate change and rising sea levels should be of serious concern to all Governments around the world.  The climate is changing and many dry regions are likely to get drier and wet regions wetter (Hoff, 2003).  Hoff states that the world’s hydrological cycle is said to be intensifying and extreme weather events increasing. 

 It is now accepted that climate change due to man's actions is occurring, and measures need to be taken to control the rate of climate change and the impact from climate change. 

There is a lobby in the UK for nuclear power because it does not impact on climate change, despite the long-term danger from radioactive waste.

According to the Kyoto Protocol (Dec 1997), there are six gases  listed greenhouse gases (GHG)including:  carbon dioxide (CO^₂), methane (CH4), nitrous oxide (N20), hydrofluorocarbons (HFC’s), perfluorocarbons (PFC’s) and sulphur hexafluoride (SF6).

Landfill gas typically contains 60 percent CH4 and 40 percent CO^₂ as it is generated.  CH4 has at least 21 times more effect as a greenhouse gas than CO^₂. Therefore, CH4 has got to be a key gas to address in reducing global warming. 

Reducing CH4 emissions has over 21 times the effect of reducing CO_² emissions albeit that there are considerably more CO_² emissions from industry and transport than CH4 emissions.

European Union countries, and the majority of first world countries, have legislation to control the landfill emissions and combust landfill gas.  When landfill gas is combusted the CH4 is converted to CO_². 

However, some countries do not have legislation requiring the combustion of landfill gas, and landfill gas vents to atmosphere, with a greater impact on global warming. 

These countries qualify for the purchase of emission reductions (ERs).  At present there is a demand for ERs which exceeds the supply, and the income received from ERs for landfill gas combustion can fund the extraction and utilisation of the gas, with additional income to the authority.

eThekwini Municipality's Durban Solid Waste (DSW), operates three active landfill sites at Bisasar Road, Mariannhill and La Mercy. 

eThekwini Municipality recognised the need to control landfill gas emissions at Bisasar Road and Mariannhill  respectively as these sites are in and near to urban areas and already have some active landfill gas extraction and flaring. 

However, eThekwini Municipality also recognised an opportunity for income from selling ERs to fund the management of the landfill sites as well as conservation and social improvement.

Consequently, during the World Summit on Sustainable Development hosted by South Africa (WSSD, Johannesburg, 2002), officials from the Prototype Carbon Fund (PCF), a fund organisation managed by the World Bank, approached DSW to propose the development of a landfill gas utilisation project. 

Because of DSW’s advanced research collaboration with the University of KwaZulu-Natal Natal into the management of landfill gas emissions (Trois et al, 2001),  eThekwini Municipality were the first South Afrcian municipal authority to be approached by the World Bank. 

The PCF fund receives contributions from several international corporations as well as national governments worldwide namely Canada, Finland, The Netherlands, Norway and Sweden (PCF, 2002). 

Following 2002, DSW developed, negotiated and agreed on an Emissions Reduction Trading Agreement (ERTA) with the World Bank and PCF, which was signed off in June 2004 in Washington. 

DSW are now progressing with the implementation of their ERs schemes, with new landfill gas management works at the landfill sites.

(Note:  the ERs for Bisasar Road are dependent upon final agreement of an Environmental Impact Assessment (EIA).)

2. The Project Sites

Current landfill gas collection and flaring projects constructed at the Bisasar Road and Mariannhill landfills only manage some 7 percent of the total gas yield.  This proposed landfill gas utilisation project will realise the collection and destruction of in excess of 70 percent of the landfill gas from the sites.

2.1 The Bisasar Road Landfill Site

The 21 million cubic metre capacity Bisasar Road landfill was first established in early 1980 and is expected to serve the waste disposal needs of the City of Durban for another 15 years. 

Bisasar Road is arguably the busiest landfill site on the African continent, accepting a daily average of some 3,500 tons of municipal solid waste, which peaks at 5,200 tons. 

There are currently 13 operational wells at the site and DWS predicts that operations will allow the installation of 20 new wells by December 2004. 

Waste deposition will also see 4 of 13  currently operational wells covered, giving a total of 29 operational wells by December 2004.  

More wells will be provided as waste is disposed and the site is progressively restored from south to north. 

Some of the phase operations will also see the construction of temporary wells that will be covered by tipping in later years. 

Wells will be provided at around 50m spacings and given an active site area of 350,000m²; the site is large enough to accommodate 130 wells. 

The final wells will be installed by 2016.

2.2 The Mariannhill Landfill Site

The Mariannhill Landfill Site was opened in July 1997 and is considered by DSW to be a 'New Generation Landfill' (Strachan   et al, 2002). 

This 4,4 million cubic meter landfill has been constructed to 'text-book standards', being well screened from the public eye by the natural topography and the established growth of numerous large trees in the peripheral buffer zone. 

The site receives a daily average of some 700 tons of municipal solid waste.  A landfill gas extraction scheme, comprising six gas wells, linked to a 500Nm3/hr flare unit, has been installed on the site. 

The site is currently producing around 170m3/hr of landfill gas.  The Mariannhill Landfill Site has been approved as a National Conservancy Site (Strachan et al, 2002).

2.3 The La Mercy Landfill Site

DSW has operated the La Mercy Landfill Site since 1996.  Before this it operated by the designated local authority as an open dump.  The site is unlined, situated on a sandy clay soil and comprises two cells. 

The projected landfill closure date of La Mercy is 2006.  The total available surface area of this site is     72 000m², as opposed to the 44 hectare and 18 hectare landfills of Bisasar Road and Mariannhill respectively.  The site receives about 300 tonnes of municipal solid waste per day.  Historical data suggests that prior to 1996, approximately       600 000m³ of waste was in place.  By April 2004, approximately 1.15 million cubic metres of refuse will be in place at the landfill.

3. Gas Model and Gas Predictions

3.1 Gas Generation Models

Two landfill gas generation models were used to assess gas generation at the sites: the Environment Agency GasSim model and the Enviros model. 

The Environment Agency in the UK  developed a gas circulation model which was trialled and  released in 2002.  Enviros developed a gas generation model in the early 1990s with Oxford University that has been used for a range of projects around the world.  The Enviros model was developed from six years of research undertaken in collaboration with Dr Alan Young of Oxford University which culminated in DoE project CWM040/92 entitled Modelling Landfill Processes.

The full report is available from: http://users.ox.ac.uk

Gas generation for Bisasar Road and Mariannhill was assessed against the two models, and gas generation at the La Mercy Landfill Site was assessed against the GasSim model.  The GasSim model was used for the La Mercy Landfill Site and it was decided to use the results from this model as they would be more conservative than those results using the Enviros model.  

The rate of gas production at any time is a function of a number of variable factors, inluding:

• Composition and density of the waste.
• Age of the waste.
• Moisture content of the waste.
• Temperature within the landfill.
• Availability of nutrients.
• pH/alkalinity of leachate.

Although each of these factors is reasonably well understood, the inter-relationships between them are not, so it is not possible to describe the relationships with any certainty.  For effective landfill gas management it is necessary to assess the  potential of future gas production to predict the pattern and rate of gas extraction.

3.2 Gas Predictions

The accuracy of the model predictions are dependent upon the accuracy of the input information; that is, waste arisings, types, moisture content, compaction, infiltration, and so on.  The Enviros model predicts a peak of some 30 percent more than the GasSim model, although it allows for a more rapid decay curve after the peak.  The GasSim model has been used to calculate ERs as it is more conservative.

3.2.1 Bisasar Road

The GasSim model predicts a peak generation of 7,600m³/hr in 2014.  There are existing wells in old waste to the north of the site.  Gas is currently being extracted from these at 350m³/hr, taken as the baseline.  It is predicted that the baseline yield  will reduce in accordance with the GasSim model. 

A yield of 50m3/hr for a newly constructed well at Bisasar Road has been taken.  The landfill and wells are relatively deep.  However, the gas yield from the wells will decrease exponentially over time and is expected to fall to a yield of about 30m3/hr after 20 years.  Wells will be maintained and progressively replaced as needed during their life.  The maximum achievable extraction efficiency of the gas system is assumed to be 80 percnet of the gas produced.  Gas production and utilisation for Bisasar Road is summarised in Table 1, section 5 below.

3.2.2 Mariannhill

Waste will continue to be deposited at Mariannhill beyond 2024, and it is predicted that 1775m3/hr will be produced by 2024.

It is predicted that newly constructed wells will yield 50m3/hr.  The landfill and wells are relatively deep.  However, the yield for these wells will decrease exponentially and follow a similar trend to the wells at Bisasar Road.  The yield from the wells has been calculated in the same manner as Bisasar Road.

3.3.3 La Mercy

Wells at La Mercy will be installed to extract the gas in the southern area of the site in 2004 and the northern area in 2006.  The waste at La Mercy site is shallower than Bisasar Road and Mariannhill and a theoretical maximum of 30m 3/hr gas yield for each well has been taken.  Gas production at La Mercy is calculated to peak at 770m3/hr when the site is closed in 2006.  Given that there will be 25 wells installed by 2006, the theoretical maximum yield for each well given 80 percent efficiency of gas collection can be calculated to be 23m 3/hr.  After capping is complete gas extraction is taken to follow the gas production model curve at 80 percent efficiency.

4. Utilisation Options Assessment

4.1 Options

There are three options for landfill gas utilisation, namely direct end use, electricity generation, or indirect end use.

The most cost-efficient process for landfill gas is direct end use as a fuel.  Landfill gas has been used as a direct end use replacement fuel in cement and brick kilns, bitumen production, leachate treatment, district heating (Stegman, 1996).  Direct end use requires an end user within 2 to 3km of the landfill site, preferably with a continuous demand similar to the gas energy, and preferably with a process that can use dirty, low calorific value gas.

The majority of landfill gas utilisation projects around the world are electricity generation by containerised reciprocating engines.  There have been landfill gas electricity schemes in the UK since 1984.  Lean burn, turbocharger reciprocating engines, for example Jenbacher, Caterpillar, Deutz, have now become established as the main suppliers.  Dual fuel engines, supported by other gas, were used in the late 1980s, early 1990s, but these are not as cost-effective as lean burn, single fuel engines.

A rule of thumb for sizing landfill gas engines is that 1MW will be produced by 670 m3/hr landfill gas at 45 percent CH4 (Couth 2000), although engines are becoming more efficient.  Electricity can also be generated using gas turbines.  Whilst gas turbines are more efficient than reciprocating engines, they require a greater supply of gas (greater 2500 m3/hr), greater clean up of the gas, a much high input pressure, and are consequently less flexible than reciprocating engines for landfill gas utilisation.  Puente Hills, one of the largest landfills in the USA, burns landfill gas to produce steam and drive a steam turbine.

There have been a number of projects around the world to upgrade landfill gas to a similar energy value to natural gas in Holland (Coups et al,1996), the USA (Monteirs, 1995), and Brazil (Roe et al, 1998).  To do this, landfill gas needs to be dried, and the CO_², sulphur and halogenated components need to be removed.  However, these have not been significantly developed to date. 

4.2 Assessment

Bisasar Road landfill is near to a commercial area and an investigation was made into whether any industries could utilise the gas.  None was found.  Hence, electricity generation is being progressed.

Mariannhill and La Mercy landfill sites are more rural and the only option for them is electricity generation.

It is predicted that sufficient gas will be extracted for at least 6MW at Bisasar Road and 1.5MW at Mariannhill.  This will be provided by modular units, built up over time.  It is considered financially viable to install an engine at La Mercy and provide electrical connections to the site.  A 0.5MW engine is proposed, but this will be reviewed after the gas extraction system has been commissioned.  The units will not be installed until the gas yield has been confirmed by extraction.

5. Certified Emission Reducation (CER)

CER, in terms of carbon dioxide equivalent, for each of the three sites is shown below.  The total CERs for the three sites are given in the Summary at the beginning of this paper.

Figure 1:   CER Generation Profile at Bisasar Landfill

Figure 2:   CER Generation Profile at MarainHill Landfill

Figure 3:   CER Generation Profile at La Mercy Landfill

Figure 4:   CER Generation Profile, total for 3 landfills.

Table 1:  Total proposed emission reductions (ER) for the Durban CDM project

Note:  ER Figures shown represent tons of CO2 equivalent that are predicted 21 years from 2003.

6.  Financial Viability

6.1 CERs and the PCF

The CDM is one of three Flexibility Mechanisms under the Kyoto Protocol, along with Emissions Trading and Joint Implementation (JI).  The CDM allows developed and industrialised countries (Annex 1 countries) to invest in projects in developing countries that would realise GHG emission reductions (SACAN, 2002).  Industrialised countries may then use such Certified Emission Reductions (CER), generated under the CDM, to contribute to compliance with their own emission reduction commitments.

In South Africa, electrical power is mostly generated by the parastatal Eskom through coal-fired power plants.  Durban currently purchases electrical power for an overall unit purchase price of R0.12 per KWh (SA Rand – approximately $0.015 US).  Following several investigations into the utilisation of landfill gas by DSW, no project has been deemed to be financially viable.  With particular regard to electrical generation from landfill gas, a unit-selling price of no less than R0.25 per KWh could be offered to the electricity department.  Indeed, this would require a financial 'top-up' of no less than 100 percent for any proposed landfill gas-to-electricity-generation project.

6.2 PCF, World Banking

ER credits will however make the utilisation of landfill viable, and successful development of this project should provide an internal rate of return in excess of 25 percent for the City.  The project agreement will be for the sale of 3.8 million tons emission reductions, or also referred to as 'carbon dioxide equivalents (CO2eq)' at the rate of $3.95 per ton over the maximum period of 21 years.  Of this amount, it is agreed that $0.20 per ton must be credited to a social benefit.  In this regard the PCF has agreed that the total amount that the project will generate for the social benefit project may be payable 'up front'.  The City is to identify suitable community projects for this social benefit payment, which are to meet with the City’s sustainable development criteria.  Additionally, the project will facilitate the allocation of capital funds to enable the extraction of the landfill gasses which have caused distinct odour concerns to surrounding communities (Stretch et al, 2001).

Financial projections for the delivery of 3.8 million tons of ER, indicate a total project cost of R150 million which is the summation of capital expenditure of R64 million and operating costs of R86 million.  The anticipated revenue from the project is R205 million which is the summation of ER sales to the PCF totalling R114  million and R91 million from the sale of electricity to the grid.  This would realise a net profit to the City of R55 million over the expected agreement period of 12 years.  However, the project may produce ongoing significant profits by way of the sale of Certified Emissions Reductions (CER) to other buyers on the world market.  The preliminary project design works have already been completed and procurement of the gas management and utilisation contracts is asked to progress.

7.  Conclusions

Subsequent to South Africa’s ratification of the Kyoto Protocol, and since South Africa’s recent signing of a Host Country agreement, the availability of 'Carbon Finance' has realised the financial viability of landfill-gas-to-electricity-generation projects in Africa.  Methane gas, a major constituent of landfill gas, is a distinctly serious greenhouse gas and such projects, if realised, will assist towards global emission reductions (ER) of GHG. The City of Durban is set to pioneer the CDM-pathway with what may be Africa’s first CDM project, with a first Landfill Gas to Electricity generation project for the continent. 

Indeed the project is a prototype, which is suitably the name of the World Bank’s fund organisation that is to provide 'Carbon Finance' for this project, namely The Prototype Carbon Fund (PCF).  The project engineering and associated project financials are well established, and the City has signed Emission Reductions Purchase Agreement (ERPA) with the PCF.  The project, incorporating three landfills will harness landfill gas to be fed to spark-ignition electrical generating units for a planned power production of  over 8MW.  It is anticipated that up to 7.7 million tons of certified emission reductions (CER) could be realised by the project, albeit that the PCF agreement is for the purchase of 3.8 million tons of ER.  Indeed, it is hoped by all parties that the project will become a CDM project, following approval by the CDM executive board of the UNFCCC, and kick-start similar projects on the African continent. 

Acknowledgements

The authors would like to gratefully thank the honourable Mayor of Durban and the eThekwini Municipality, councillor Obed Mlaba, and the City Manager, Dr Michael Sutcliffe, for their invaluable support to this project.  Many thanks to the project team members who were the 'engine room' in putting this project together, namely Dr Debra Roberts, Steve Harms, Charles Donovan, Trevor Palmer and John Paley.

References

Coops, Luning, Roks.  Upgrading landfill gas by using membrane technology.  Sardinia Fifth International Landfill Symposium, Proceedings.

Couth B (2000).  Landfill Gas:  Generation and Modelling.  Proceedings of International Training Seminar on Control, Management and Treatment of landfill Emissions. University of Natal, Durban, SA, 6-8 December 2000.

Hoff H (2003)  Planning for Climate Change?  Publication in Water 21.  IWA Publishing, London, February 2003, pp 43-44.

Monteirs.  Landfill gas utilisation as vehicle and household fuel in Brazil.  Landfilling of waste: biogas.  E&FN Spon 1996. 

PCF (Prototype Carbon Fund) 2002.  PCF Annual Report 2002.  World Bank’s Prototype Carbon Fund, Sept. 2002, Washington, USA).

Roe, Reisman, Striat, Dourn (1998).  Emerging technologies for the management and utilisation of landfill gas.  US EPA

SACAN (South African Climate Change Network) (2002).  CDM.. “Can we justify selling Africa’s atmosphere”.  Article publication in Climate Action Network.  SECCP, July 2002.

Stegmann (1996).  Landfill gas utilisation: an overview.  Landfill of waste biogas.  E&FGN Spon 1996.

Strachan L, Rolando A and Wright M (2002).  Rescue, Reinstate and Remediate – Landfill Engineering Methods that Conserve the Receiving environment.  Proceedings Wastecon 2002, International Congress, IWMSA, pp 443-451.

Trois C, Strachan L and Bowers A (2001).  Using a Full Scale Lined Landfill Cell to Investigate Waste Degradation Rates Under a Sub-Tropical Climate.  Proceedings Sardinia 2001, Eighth International Landfill Symposium, CISA, Cagliari, Italy, Vol II, pp 51-57.