Thomas Sandberg and Knut Bernotat

8.1. AIMING AT SUSTAINABLE ENERGY SYSTEMS

The share of renewable energy is high in the Swedish energy system. In 2001, 177 TWh or 44 per cent of the total energy consumption in the country came from renewable sources. In the residential, service and industrial sectors, this share was as high as 58 per cent. Since 1991, bioenergy is the largest renewable source in Sweden and, in 2001, 98 TWh were generated from this source. This compares with 79 TWh from hydro and 0.5 TWh from wind (Swedish Energy Agency, 2002a; see also Ling, Chapter 3).

Even if these are impressive figures, some 122 TWh remain to be converted to renewable sources, not to mention the other 92 TWh in the transport sector. Scenarios developed for the year 2050 indicate that this is a manageable task for Sweden (Elforsk, 1996; SAME, 1999). The crucial point is to speed up the process and to make it cost efficient. Although the resources and technologies are there, administrative, economic and political structures delay the shift towards a sustainable energy system.

District heating supplies 46 TWh of the 93 TWh heat consumption in Sweden today. Nearly all this energy emanates from large-scale units connected to large-scale district-heating systems. Some 32 TWh are generated from biomass. Due to the large availability of electricity from hydro and nuclear sources, only 5 TWh of electricity is being produced in combination with heat. We argue that district heating, supplied by combined heat and power (CHP) production based on bioenergy, holds an important key to the shift towards larger use of renewables in Sweden in the next two decades. Most probably, this is also true for many other countries with moderate climate, where there will always be a large need for heating.

There are many ways to enhance the utilization of bioenergy in Sweden. In general, this includes:

• Continuing the conversion from fossil fuels to biofuels;

• Increasing the power production in sites where CHPs are installed and fueled by biomass;

113 Bioenergy — Realizing the Potential

© 2005 Dr Semida Silveira Published by Elsevier Ltd. All rights reserved.

• Introducing power production in sites where only heat is produced from biomass;

• Enlarging existing district-heating grids; and

• Building new district-heating grids and CHP units fueled by biomass.

Since large cities and many towns in Sweden already have a district-heating system, the remaining potential is in smaller places with a few thousand down to even less than one thousand inhabitants. Therefore, in this chapter, we focus on small-scale district heating grids supplied by small-scale CHP fueled by biomass. Our task is to calculate the potential for such systems in Sweden.

We first present a method to estimate the potential for small-scale district heating. The essence of the method is to identify clusters of buildings where the heat demand is large enough to justify small grids. We use this method to evaluate the potential of a small region in southeast Sweden, and of three counties in different parts of the country. Finally, we extrapolate the results to make a rough estimation of the potential for new district heating systems in the country as a whole, and to evaluate the potential generation of electricity from the CHP units.

The Clean Development Mechanism (CDM) creates an institutional base for a direct participation of developing countries in the implementation of the Kyoto

Protocol. Although no emissions reductions target has been negotiated to developing countries, their involvement in climate change activities is essential since these countries are expected to have a huge increase in greenhouse gas emissions in the coming decades. Through the CDM, developing countries can become fully involved in mitigation measures, and thereby, important actors in the formation of carbon markets. This shall help pave the way to more ambitious targets and new commit­ments at a later stage.

The two overall requirements of CDM projects is that they should contribute both to the reduction of emissions according to a baseline or predetermined scenario, and to sustainable development according to priorities and strategies defined by the host country. The baseline gives the trajectory of expected emissions in the absence of the project. The emissions reductions have to be quantifiable and measurable, and should result in improvements in relation to the baseline. The contribution to sustainable development and to reduce emissions entails the issuing of certificates, CERs, which can be traded internationally after proper validation of the project, and verification of the emissions reductions actually achieved. Figure 12.1 summarizes the key requirements of CDM projects.

Various CDM projects are being presently implemented around the develop­ing world. This is contributing to the development of methodologies to define base­lines and determine actual emissions reduction. While baselines seem to be one of the most difficult issues around the CDM, once determined, the measurement of emissions reductions is a rather technical matter. It is less clear, however, how the sustainability dimension associated with these projects will be more closely defined and monitored. In principle, the contribution of the project to sustainable deve­lopment will be measured in relation to the host country’s development priorities and strategies. On the other hand, the long period for CER accreditation in a CDM project may be in contrast with the nonlinear dynamics of socioeconomic develop­ment within the same time frame, and the still very recent experience of introducing sustainability criteria in development strategies and projects.

Figure 12.1. Key requirements of CDM projects.

A combined cycle plant based on a PG6101(FA) gas turbine, such as the one con­sidered in this study, and following the hypothesis assumed, consumes about 500 thousand Nm3/day of natural gas operating at full load basis (about 430 Nm3/day for an average capacity factor of 0.85). Thus to guarantee full operation of a 100 MW plant, some 540 thousand Nm3/day would be needed. Table 9.6 summarizes the amount of natural gas that can be displaced per set of 100 MW power capacity for each cofiring alternative analyzed in this study. Results for Case В correspond to the best case from the point of view of capacity, i. e. 101.7 MW of net capacity, for 61.9 per cent substitution of natural gas on mass basis.

To give a perspective of this contribution, we look into the present situation in Brazil. The Brazilian government has recently decided to support the installation of almost 17 GW of thermal power capacity, totalling 49 plants, most of them designed to fire natural gas. Of this total capacity, 6.5 GW are planned in industrialized sites of the State of Sao Paulo, not far from the regions where there is a large con­centration of sugarcane mills. The natural gas demand to allow the operation of 6500 MW new capacity in the State of Sao Paulo is estimated at 25 to 26 million Nm3/day, taking into account the predicted average annual capacity factor and actual natural gas to electricity efficiencies (in round numbers, larger than the performance figures used in this article). This natural gas volume is quite substantial as a share of the capacity of the brand new Brazil-Bolivia natural gas pipeline, the main source of natural gas supply for the years to come.

The adoption of a Case C strategy would allow a maximum displacement of natural gas of about (124.6/577.0) x 25-26 million Nm3/day = 5.4-5.6 million Nm3/day. With the strategy that corresponds to Case B, the maximum volume of natural gas that could be displaced would be (345.6/577.0) x 25-26 million Nm3/day= 15.0-15.6 million Nm3/day. On the other hand, theoretically, a Case A

strategy would allow 100 per cent natural gas displacement. It is clear from the numbers presented that cofiring biomass and natural gas could make the natural gas market more flexible, without drawbacks to electricity generation.

Sugarcane production in the State of Sao Paulo is estimated at 180 million tons per year. With this level of production, some 23.2 million tons of sugarcane trash could be recovered (50 per cent of the amount available, owing to topographic constraints; sugarcane trash availability is equivalent to approximately 25 per cent of sugarcane mass). The full availability of bagasse is estimated at 46.8 million tons/ year (13 per cent fiber content and 50 per cent moisture), the ordinary surplus being about 10-15 per cent of the total availability. Achieving 6500 MW capacity, full implementation of the Case C strategy would demand 18.7 million tons of biomass per year, while the Case В strategy would require 33.9 million tons/year. Nowadays, trash is essentially burned at the field before sugarcane harvesting. For bagasse, there is not a market able to consume all the existing surplus. Hence, from the point of view of biomass availability, there is no particular constraint regarding the imple­mentation of the cofiring alternatives analyzed here.

From the economic point of view, the preliminary results indicate that Case В can be considered as a reasonable alternative as the cost of electricity produced is kept at an acceptable level, and the investment IDR is not reduced to any large extent when biomass contribution is considered. If the biomass plant can be built mainly with equipment manufactured in Brazil (thus at lower capital cost), Case C is the best option, as it allows a reduction on the cost of electricity produced while enhancing the investment IDR. According to the results, to substitute biomass for natural gas in BIG-CC power plants (Case A) is not a good alternative as some amount of natural gas allows improvements in the system economics. Obviously, the oppor­tunity to generate carbon credits from cofired plants would make a substantial difference on the economics of such alternatives.

The feasibility of Case В and Case C could be further improved with larger power units, taking advantage of economies of scale and, consequently, reducing the capital costs per unit energy generated. Strictly speaking, the location of the power plant would be a matter of concern regarding biomass transportation costs. The same is true regarding plant size — as the scale of the plant increases, costs related to logistics also increase.

The Brazilian iron industry is divided into three main groups: (A) independent small pig iron producers; (B) large integrated steel mills using charcoal or coal coke; and (C) integrated coke-based steel mills. The total production of pig iron in 2000 was 27.7 million tons, of which 14 per cent were exported and the rest consumed in Brazil (IBS 2001). Table 14.1 shows the pig iron production in Brazil by producer.

The first group, small independent pig iron producers, in which the sponsor of the Plantar project operates, is the most numerous. There are about 40 independent firms producing pig iron in the State of Minas Gerais alone, with approximately 80 blast furnaces. These companies are mainly focused on the supply of iron to foundries and mini-mills in the international market and replacement of scrap used in electric arc furnaces of large steel producers in the domestic market (Group C as shown in Tables 14.1 and 14.2).

The plants of small independent producers usually have established capacity between 60 and 400 thousand tons per year, which is much smaller than those of the producers in the other two groups. Technological and economic constraints render unfeasible the conversion of small blast furnaces to use coke as has been the case among large producers. As a consequence, this sector remains dependent on charcoal as the main source of raw material for iron reduction.

The second group comprises four large private companies that originally produce steel mainly from charcoal: Acesita and Belgo-Mineira, which previously used both coke and charcoal as a reducing agent; and Mannesmann (now V&M do Brazil) and

Gerdau, both still reliant on charcoal. This type of enterprise, charcoal-based steel making, is only found in Brazil. Because of their production volumes (which range from 600000 to 4.1 million tons of steel per year), they can make the conversion from charcoal to coke, which indeed has been accomplished by some companies. This group is, thus, the most responsive one to market factors in relation to the reducing agent (charcoal or coke) used.

The third group, integrated coke-based mills, currently account for 74 per cent of total pig-iron production in Brazil. This group comprises five large-scale enterprises (CST, Usiminas, A5ominas, Cosipa, and CSN), previously parastatals that have been privatized since the early 1990s. The current trend has been towards an increasing concentration of the industry in integrated mills. These companies produce most of the pig iron produced in Brazil to supply their own steel mills (see Tables 14.1 and 14.2).

The forest legislation has forbidden the use of charcoal from native forests after 1992 (Forest Law of the State of Minas Gerais number 10.561 on 27.12.1991 and Decree 33.944 on 18.09.1992)[18]. Since then, the industries began to reduce the use of

charcoal from native forests and increase the consumption of charcoal from forest plantations. However, such charcoal was mostly produced from eucalyptus forests that were planted with tax incentives from the Federal Government between 1966 and 1986. Table 14.3 depicts the total decrease in charcoal utilization between 1988 and 1997, as well as the balance change between charcoal from indigenous forest vis-a-vis planted forests. Nonetheless, in spite of current legal and policy provisions, Brazil still faces great lack of fuelwood plantations and law enforcement in what concerns native wood usage. Even though local and state authorities have improved inspection and surveillance, charcoal manufacturing is often based on deforestation which also leads to intensive methane emissions.

According to statistics from IBAMA (Brazilian Institute for the Environment and Renewable Natural Resources), the stocks of existing forests can supply the market demand for charcoal for the next seven years. On the other hand, a recent study from BDMG (Development Bank of State of Minas Gerais) indicated demand for 110000 ha of forests in 2007 while no forests are being planted to supply charcoal markets. In fact, regulatory, operational and economic barriers are leading to the decline of wood-plantations which contrasts with the effective demand for charcoal, and increases pressure on native wood sources.

Eucalyptus forest plantations in Brazil need approximately seven years to mature. Thus there is the need to plan in advance to guarantee the survival of the charcoal producers on a sustainable basis. Forest plantations with selected clones and high productivity, aimed at re-establishing the stocks of charcoal can have a positive effect in changing current trends and foster a larger use of charcoal in pig iron industries. This can be done following the environmental sustainability principles while also guaranteeing employment for many charcoal producers.

14.2. BASELINES

The Plantar project is based on three distinct but inter-linked baselines, and an additional pilot project of rehabilitation of native vegetation as follows:

• The forestry component, which involves the establishment of new Eucalyptus plantations;

• The carbonization process component, which involves altering the design of carbonization kilns and/or the carbonization process to reduce the emissions of methane;

• The industrial component, which consists of the avoidance of coke in the production of pig iron by using charcoal from sustainable forests;

• The pilot project on rehabilitation of native vegetation in the Brazilian cerrado.

The baseline scenario for the project is based on what would have happened in the absence of the project activities. In this case, the baseline scenario would be the gradual death of the charcoal-based independent pig iron producers, giving place to increasing production based on coal in large mills. The latter would gradually take over the market share controlled by small pig iron producers. In addition, the existing planted forests will not be replanted after the third cycle of rotation and, most probably, the land will be used for pasture, which is the most common activity in the region.

The Plantar project scenario allows for the use of sustainably produced charcoal as the reduction agent in the production of pig iron, avoids the absorption of the charcoal-based market share by the coke-based pig iron production, and also avoids GHG emissions. The CDM framework allows the project activity to be cofinanced through the sales of carbon credits, protecting from the potential loss of the industry and market shares of small charcoal-based pig iron producers. Moreover, the forestry activities to supply charcoal to Plantar’s mills are based on new high yielding plantings.

Figure 14.1 shows a comparison of two routes to produce pig iron and demonstrate the main steps of the production process utilising coke and charcoal. In both cases, there are greenhouse gas emissions in the carbonization process. The types of kilns used by Plantar (currently approximately 2000 kilns) and other charcoal manufacturers in Brazil produce emissions of methane. Plantar will invest in the refurbishment of its kilns, and in the improvement of the carbonization process to reduce the emissions of methane to the atmosphere.

Finally, Plantar will initiate a pilot project to manage some of its lands to enable the regeneration of the cerrado and other native vegetation in lands that were previously planted with Eucalyptus or were used as pasture. If successful,

Plantar intends to expand this component of the project to other lands elsewhere. The balance of emissions reductions expected from the whole project is shown in Table 14.4.

The practice of clearing and burning the soil has been used in Brazil since colonial times. Also in sugarcane production, burning has been commonly used as it increases the throughput in both manual and mechanical harvesting. Producers utilizing green cane harvest practices report 30 to 40 per cent lower daily tonnage for unburned cane when compared to burned cane (Ripoli et al., 1990). The sugarcane burning practice is now undergoing severe restriction due to increasing urbanization, particularly in southern parts of the country. Still, in the State of Sao Paulo, green cane harvesting is only practised in a 1 km radius around the cities as a result of law enforcement (Governo do Estado de Sao Paulo, 1988).

The reason for preventing the burning of sugarcane fields is to avoid emissions to the environment (i. e. pollutants such as CO and particulates), which have impact on human health (i. e. respiratory illnesses) and human amenity. Furthermore, valuable cane residues that could otherwise be utilized for energy purposes are lost in the burning process. Long-term trash mulching can reduce nitrate fertilizer applications by 40 kg N/ha, mainly as a result of reduced nitrate leaching (Vallis et al., 1996).

Field burning also results in sucrose losses by exudation on the surface of cane stalks. Ripoli et al. (1996) have found ethanol losses in the range of 59 to 135 liters/ha due to such practices. Work done by Fernandes and Irvine (1986) on commercial sugarcane fields of several companies indicated that the actual sugar yield was below the potential existing in the field, both through manual cut (-17 per cent) and through chopper harvester (—21 per cent). These losses occurred in burning, harvesting, loading, transportation, and reduction in cane quality.

The interest in mechanical harvesting grew strong in the 1970s due to studies that forecasted labor shortage (Stupiello and Fernandes, 1984). Mechanization efforts did not succeed at that time and the interest eventually faded in the 1980s, partly due to the deterioration of the Brazilian economy. By the middle of the 1990s, the question had regained interest (Furnari Neto et al., 1996). The main difference in studies done today is the emphasis on reduction of production costs, mechanical harvesting being one step in this direction. Today’s cost for manual harvesting and loading of burned cane may exceed US$ 4.00/ton (Coletti, 1997) while mechanical harvesting hardly reaches US$ 2.00/ton (Lima, 1998)[8]. In the case of green cane harvesting, data is still unreliable but there are indications that manual cutting exceeds US$ 6.00/ton while mechanical harvesting is around US$ 3.00/ton.

Both the ergonometric and economic arguments indicate that green cane har­vesting is likely to foster mechanization of harvesting practices in Brazil. A signifi­cant expansion of mechanized practices, however, will depend on improvements to the available mechanical harvesting technology. This includes the considerations listed below.

• The machine throughput and harvesting costs should not be but marginally affected by the amount of trash.

• It should be possible to remove the trash from the field for other purposes, such as energy conversion. So far, there are no adequate cane varieties and agro­nomic experiences to manage trash blanketed cane fields (Sizuo and Arizono, 1987).

• A percentage of the straw should be left in the fields for weed control and moisture conservation in cases where agronomic management techniques are well established.

• The present system of whole cane harvesting should be maintained to avoid unnecessary investments associated with the change to chopped cane as well as to avoid raw material (sucrose) loss associated with the chopping and cleaning processes, which represents an unacceptable technological step back in the Brazilian context.

The present field experience with whole cane harvesters together with recent develo­pments on whole cane mechanical cleaning (Tanaka, 1996) as well as on machine right angle turning and pilling (Braunbeck and Magalhaes, 1996) added to the known potential of computerized engineering resources applied to machine design, anticipate the feasibility to develop a whole cane harvesting equipment taking into account the aforementioned features. Meanwhile, the mechanical harvesting expansion faces financial and technical constraints such as: shortage of skilled labor; bad field lay­outs and poorly performing harvester technology for the existing fields; lack of capital; existing whole cane transportation and reception at the factory different from the emerging chopped cane system; and design for maximum 12 per cent soil slopes for present harvesters which limits its use to about 45 per cent of the sugarcane areas.

Despite the country’s large production of sugarcane, mechanical harvesting is still hardly employed in Brazil (see also Table 6.3). Although there is no precise figure on the number of harvesting machines in operation today, this number should not be greater than 600 machines harvesting approximately 50000 tons/machine-season making a total of 30 x 106 tons. This represents 10 per cent of the total 300 x 106 tons harvested in the 1997/98 season. Frequent reference is made to the existence of quite high mechanization, but that relates to isolated cases such as Usina Sao Martinho, where 89 per cent of the cane was mechanically harvested already in the 1993/94 season.

Nevertheless, mechanical harvesting is growing fast in the State of Sao Paulo. This is not only due to the good topography of the state but also due to the well — developed road network and availability of skilled labor to operate a mechanized system. When cane producers of other states such as Goias and Mato Grosso implemented mechanical harvesting, they faced serious difficulties in hiring adequate labor to operate and maintain the machinery. It takes several years until the har­vester’s fleet can reach a production of 400 t/machine-day as the season average in 24h/day operations. Usina Sao Martinho, State of Sao Paulo, has exceeded productions of 600 t/machine-day, greatly due to skilled labor and adequate infrastructure, while Usina Sta. Helena, State of Goias, achieved the average harvester throughput of 400 t/machine-day first after 6 years operation.

Chopped cane has higher dirt and trash content. Unloading of chopped cane frequently has lower priority at the mill as a function of its lower quality. It creates a transportation shortage to the harvesting fleet and increases the cost of the operation. Lower cane quality comes mainly from inadequate technology at the machine base cutter which consists of two flat disks with approximately 900-mm diameter each. This defines a 1800 mm wide plane and requires a perfectly levelled soil for the disks to operate very close to the surface without cutting the soil. Recommendations for efficient operation of base cutters require flat and levelled land, but this turns out to be insufficient since the problem remained in Australia even after many years (Ridge and Dick, 1988).

Brazilian undulated cane areas inject large quantities of soil into the harvester. Though it is removed inside the machine, about 0.5 per cent of the soil still remains in the cane and this has an impact in the cane processing at the factory. The soil

Table 6.3. Comparative features of sugarcane harvesting technologies used in Brazil

Type of Harvesting

Parameter Semimechanized Mechanized — chopped cane

Stalk and tops cutting with cane bundling

<1%

600 t/machine-day; loading may achieve 700 t/machine-day

US$ 1.5/t

Requires trained labor; losses of raw material originated from base cutting and elevating rolls; traffic between lines; two passes by the harvesters; damaged stalks by the base cutter and transporting rolls

Minimum incidence of labor (only in operation and maintenance); independence of cutting and transporting operations which eases the operation management; increases

content of hand cut cane will not exceed 0.15 per cent when loaded with properly operated rotary push-pilers. Summarizing, the chopper harvesters present several critical points of cane losses such as the double disk base cutters, the feed rollers, the chopper and the cleaning extractors. These components are responsible for losses ranging from 7 to 15 per cent (Ridge et al., 1984; Fernandes and Irvine, 1986). The solution to this problem will arise from existing and future developments on alternative cutting and feeding mechanisms more than from insisting on extension work to further level cane fields, which creates adverse agronomic conditions for cane longevity and moisture conservation.

The technological innovation and investment capacity of the Brazilian agricul­tural machinery industry is rather small. It essentially limits itself to promoting the chopped cane technology developed abroad. There is also a technical barrier related to the potential use of machinery in areas with an unfavorable topography. Techniques, such as four-wheel steering and traction as well as steel or rubber tracks would allow to extend mechanization up to about 90 per cent of the areas which are currently occupied by sugarcane. Today’s harvesters are mainly one-row machines with high center of gravity using two-wheel traction in the rear and two-wheel steering in the front. This driving and traction configuration is acceptable for agricultural tractors in which alignment with the line of motion is not so important. In the case of harvesters, the lack of machine alignment with the crop lines leads to cane losses and frequent stops due to clogging. It would be technically possible to develop harvesters capable of operating in most of the hilly areas if present harvesting principles were simplified to allow investment on four-wheel traction and steering, still keeping the equipment economically feasible.

A successful implementation of mechanical harvesting in Brazil needs to address a series of technical issues based on topographic, agronomic and sugarcane processing conditions, typical to Brazil. Therefore, a development and economic effort is still required to improve the harvesting efficiency. Table 6.3 compares the features of sugarcane harvesting technologies being used in Brazil, which further illustrates the technological improvements needed.

Even if they have relatively low overall efficiencies, generation plants operating on conventional steam cycle are based on proven technology, refined over several decades. It is also important to note that there are many well-established manu­facturers throughout the world using this technology including some within the South Asian region. Typical capacities offered with this conventional technology vary between lOOkW and a few hundreds of MW. Reliability of these plants tends to be relatively high and the technical know-how is widespread among many users. Spare parts are widely available as the technology is well established. Considering these factors, plants operating on conventional steam cycle technology seem to be more appropriate for Sri Lanka.

Economics

According to the economic analysis presented in the report, the energy costs associated with biomass-based plants operating on conventional steam cycle techno­logy are comparable with those of large conventional gas turbine plants presently operating on auto diesel. With declining capital costs of biomass-based plants, particularly those from manufacturers in the South Asia region the overall costs are likely to come down in the near future. As a result, biomass-based electricity gene­ration can become competitive in the Sri Lanka electricity generation system where fossil-fuel-based generation has become a significant component.

We start from the demand side, evaluating the demand for heating services. The basic notion is to identify geographic areas (clusters) where the heat demand is large enough to justify installing a local small-size heat and power production. But how to identify those clusters with different residential, commercial, industrial and public buildings, and how to estimate their heat demand?

When looking for the potential demand, we need to differentiate between theo­retical and practical potential. The theoretical potential is the overall estimate of the demand for heat in a given area. It is based on the estimates for each individual building in the area. The theoretical potential includes all buildings and thus even those where it is not currently technically or economically feasible to use small-scale district heating. The theoretical potential is an important reference because technical and economic conditions change over time and move the border for feasible appli­cations. The theoretical potential also gives the individual, nonaggregated data for estimating the practical potential (Bernotat, 2002).

The practical potential in an area is defined as the total heat demand of buildings, which are technically and economically feasible to connect to a small-scale district heating and CHP. The practical potential is found by merging the theoretical potential of single buildings to larger units until a suitable size is found. Figure 8.1 illustrates the relation between the theoretical and practical potential over time.

Theoretical potential

Practical potential Year x + 10

Figure 8.1. Theoretical potential and practical potential over time. Source: Bernotat, 2002.

Figure 8.2 shows how this translates into the reality of suitable clusters when they are visualized with the support of the GIS tools applied in this study.

The actual estimation of the potential is done in two steps. First, the heat con­sumption of every single building is estimated using data from the land survey register on building type, year of construction, floor space and the precise location. The survey data on the average heat demand per square meter for buildings of different types, age and location are then added. Second, the estimated heat demand of the individual buildings in the focused geographic cluster is aggregated with the help of Geographical Information System (GIS) tools. The shape and size of the clusters within an area can be varied, as also the minimum heat demand required for the clusters in order to match preferences and predefined economies of scale1. [9]

One crucial question that remains always is what minimum heat demand is required to justify the infrastructure investment. In the clusters with more than 2 GWh heat demand, we are close to the point where, already today, it is not only technically but also commercially feasible to produce heat and power. At around 1 GWh heat demand, it is commercially feasible to produce heat if the district­heating grid is small enough. A crucial question is when power production equip­ment for such small and even smaller CHPs will be commercially available. These figures serve as an indication for the purpose of this analysis but need to be further investigated in each case, not least in relation to the grid size and the availability of biomass to fuel a CHP, as we have in mind.

The CDM project can be developed by public or private entities. The objective is to create a clear line of procedures so that participation is facilitated, and CERs can become internationally accepted and tradeable. Initially, CDM projects were mainly developed on an experimental basis by enthusiastic countries and companies that believed in the economic and environmental benefits of CDM, or wanted to take advantage of being early starters. Attitudes towards the mechanism have varied both in developing and industrialized countries, but ratification of the Kyoto Protocol has contributed to broader engagement of governments and enterprises in developing new projects.

A project becomes a CDM project when conceptualized according to the require­ments of the mechanism. A project design document (PDD) is prepared including the description of project activities and participants, project boundaries, the base­line and methodology for quantifying the reduction of emissions, expected leakages, as well as a plan for monitoring and verifying those reductions. The additionality of the project needs to be justified. This means that the project should result in emissions reductions which would not occur in the absence of the project.

The CDM project needs the approval of the host country’s CDM authority, the so-called Designated National Authority (DNA), which shall certify that the project contributes towards sustainable development. After this, the project needs to be registered with the Executive Board in order to be eligible for CERs. The Executive Board supervises the implementation of the CDM and is nominated by the parties to the Kyoto Protocol.

The project is implemented and monitored by the developers and other partici­pants, who shall collect all necessary information for the verification of emissions reduction by authorized entities. The Designated Operational Entities are the only ones in position to validate the project activities and performance, and certify the accomplishment of emissions reductions. Only then can CERs be issued by the Executive Board and, eventually, traded or used to meet commitments. Figure 12.2 summarizes the CDM project cycle. The upper boxes indicate the institutions res­ponsible for each step.

The role and level of importance attributed to CDM as part of emissions reduction efforts has varied among industrialized countries. A country can choose to use CERs as part of mitigation measures of companies in their territory, or can put a cap to how much reduction can be accomplished through CDM projects. Ideally, there should be as many projects as possible to reduce emissions as much as possible and foster sustainable development. In practice, however, industrialized countries need to also implement measures at home to enhance credibility about their

commitment to climate change issues, and as a way to foster low carbon or carbon — free production systems.

Electricity production with the use of a renewable energy source on a sustainable basis is clearly the most important contribution of the cofiring alternatives discussed here. Additionally, natural gas could be used in a more rational manner, allowing gradual changes within the energy matrix and reduction of environmental impacts. In fact, a transition into biomass for power generation can be interesting for natural gas distribution companies. These companies could maximize their take-off in the beginning of the cash flow project and further extend their supply of natural gas at a very low cost (or even no cost) as the consumer market is further developed. This transition into biomass could also be considered for countries where the market of natural gas is already well developed. Another interesting point to be considered concerns the required investment to find new reserves at high marginal costs.

One of the main conclusions of a detailed study of the cofired option presented in Case В was that cofiring could be instrumental for the market development of the BIG-CC technology in its early stages. In fact, besides the possibility of overcoming technical constraints for the very first BIG-CC units, the enlargement of the fuel heating value due to the natural gas contribution boosts the plant efficiency and, consequently, contributes to the reduction of the cost of electricity generated from biomass. The cost reduction is, to a large extent, due to economies of scale. Small biomass-fueled gasification plants can benefit from the high efficiency and low capital costs of large combined cycles without scaling up the biomass parts. However, in the medium — to long-term, as the BIG-CC is further developed and gas turbines for biomass-derived gas are redesigned, cofired combined cycles would probably be less justifiable (Souza, 2001). In the case of Brazil, successful experiences with cofiring natural gas and biomass could not only help foster BIG-CC market expansion, but also could allow a more efficient use of sugarcane residues for electricity generation.

Measures

kPa= 103N/m2

LHV = Lower heating value

MMBTU = Million of British Thermal Units

Mol = Molecular weight

MPa=106N/m2

Trash and bagasse are two fibrous materials from sugarcane, each with its own specific characteristics. Although sugarcane trash and bagasse are fibers of the same origin, their physical and chemical characteristics may differ significantly. The sugarcane bagasse has smaller particle size because it has been milled in the juice extraction process. This results in finer particle size when compared with unpro­cessed trash (Olivares et al., 1998).

Of the two, bagasse is the more studied material, because it is essentially an industrial residue that has been used for many decades as a fuel in bagasse boilers. Although it is well known that biomass fuels should have lower moisture content, the drying of bagasse has not been considered a very profitable process, at least until recently. For this reason, bagasse has been used with its original moisture content of approximately 50 per cent wet basis.

Regarding particle size, bagasse is a very homogeneous material, at least when compared with trash. Therefore, bagasse burning is more predictable a process because the biomass is composed of fibers with more or less similar characteristics, like composition and size. Dirt is also a much easier problem to solve for bagasse than trash, at least in conventional low-pressure boilers (2.1 MPa).

There is no existing technology and experiments on bagasse pelletization and briquetting of sugarcane trash. Limited information is available on bagasse pelletization but commercial bagasse briquetting has not been reported in Brazil (Bezzon, 1994; Cortez and Silva, 1997). Some technical difficulties are associated with the long-term integrity of the bagasse briquette. The bagasse high moisture content, nearly 50 per cent w. b., is considered the most negative factor when briquetting is considered. Bezzon (1994) conducted experiments at UNICAMP heating up the bagasse up to 200-300° C before briquetting (1 cm diameter and 2 cm length). The applied pressure ranged from 20-25 MPa and yielded briquettes with densities from 1000 to 1240 kg/m3. The results were promising but experiments with larger briquettes were not conducted. It is known that heating the briquette can melt lignin resulting in a fiber-binding material.

Trash is essentially an agricultural residue that is now being seriously considered for energy purposes. Tops and leaves are the main components of sugarcane trash and they are removed at two different stages of the harvesting process. Top removal is the very first operation executed on standing stalks, before base cutting. Very little information is available in Brazil concerning trash recovery and use. Very few experiments and data are reported about its characteristics and how this influences equipment design and operation. Usina Sta. Elisa in Sao Paulo has conducted some experiments on trash recovery in cooperation with Dupont and Class. Also experi­ments are currently being conducted by Copersucar on trash recovery and its use in boilers baling trash with the Class and Case machines, but no conclusive reports are available so far.

The present harvesting technology has two main drawbacks in relation to top recovery. The first one is related to the topper not being able to reach the tops of nonstanding stalks. Efforts are being made to remove tops using the extractors at the second cleaning stage of the chopper harvester. This operation is highly inefficient and top removal is directly related to cane losses. The second one arises from the fact that after cutting and chopping, a low surface density of tops is left on the field for future collections, using adapted hay technology. Raking and windrowing of tops over a bare soil surface results in high dirt contamination. Field experiments indicated soil contents of 20 kg per ton of trash recovered using hay equipment (Copersucar, 1997). Harvester design should include trash recovering from the beginning. Two pieces of existing technology need to be incorporated into a cane harvester to make trash recovering more efficient.

Tops are green, high moisture residues that require field natural drying to improve biomass quality. After harvesting the green cane, trash may be left on the soil to dry for a few days. When the trash is nearly dry, with approximately 30 per cent moisture content, it can be recovered. If left in the fields, it may increase the risk of fire or may slow down ratoon sprouting. Thus it is generally accepted that at least part of the trash should be recovered. The specialists’ recommendations on how much trash should be recovered vary from 50 up to 90 per cent. It is believed that organic material left in the fields may bring some agronomic benefits helping to control weeds and increasing the long-term soil fertility. An experiment has been reported by Molina et al. (1995), using a roller type trash baler, which processed 5.7 t/h, recovering 83 per cent of trash with 30 per cent moisture content and obtaining low-density bales with 120kg/m3.

A series of operations are required to perform trash recovery starting with raking the trash into continuous windrows after natural drying in the field. In the seq­uence, the trash must be baled to make transportation economically feasible. The commercial balers will compact up to 150 and 200kg/m3 density. The final product is supposed to resist transportation and storage in adverse climatic conditions when stored in the field. The operating costs may be the determinant in making the trash recovery feasible. The costs reported by Molina et al. (1995) varied from US$ 7 to US$ 25.00/t, depending on local conditions such as topography, infrastructure and available technology. It is a general consensus, in Brazil, that it will be difficult to compete with bagasse, but not so difficult to compete with other alternative energy resources, such as natural gas from Bolivia which is being offered in the market at a cost between US$ 2 to 3 per MMBTU. The systems tested in the last 5 years by Copersucar include various alternatives and resulted in costs below US$ 1/MMBTU in at least two cases.

Particle size is certainly a major consideration with trash because it may affect the conversion residence time in the reactor. This may also be affected by the moisture content in the particles, some of which have more moisture than others. The heterogeneous characteristics of the trash are certainly a drawback, which requires a fuel preparation procedure. Dirt in the trash is another major problem since the dirt increases the ash content and may interfere with the ash melting point and formation of deposits in the heat exchanger walls when combustion reactions take place.

In short, the existing boilers installed in sugar factories throughout the world can handle and operate better using biomass similar to bagasse. Any large variation in particle size, moisture content and dirt content will negatively affect the reactor efficiency and operation. Most likely, the most appropriated procedure is to prepare the fuel to meet the equipment requirements or, if possible, design a reactor that can efficiently operate within a larger spectrum of fuel properties. At UNICAMP an unbaling system is being conceived to unbale and feed biomass (trash) into a boiler (see Figure 6.1). In this project, the aim is to develop a technology that allows a continuous supply of biomass up to the boiler distribution system.

Boiler

Conveyor

Unbahnq system

Chopper

9§&. Remover

Figure 6.1. The UNICAMP unbaling-feeding system for biomass (trash).

The main task of the unbaling system is to cut the bale and then feed the biomass by means of the feeding screw. A chopper located at the silo’s bottom performs the cutting. The remover helps by rotating the bale and placing it against the chopper. Figure 6.1 shows the unbaling system and the chopper. The system may also include a dryer to homogenize the material moisture content.

The costs involved in the biomass preparation are not negligible. Besides the necessary investments in equipment, there is also the need for capital for the system operation, particularly if a drying system is required and a storage facility is needed. This infrastructure and economics are being examined at UNICAMP and an in-factory system is being considered during the tests. An important drawback is that there is little information in the literature about large-scale biomass preparation and handling, except in forestry, and this information is essential in this kind of projects.

The economic use of trash will depend on investigating more cost-efficient technologies to handle, transport and use the material, transforming it into a more valuable commercial product. In this sense, more research is needed not only in the conversion for electricity, ethanol and fuel gas production but also in charcoal production. Charcoal has a well-established market in Brazil and its production is still based on very traditional technologies, based on low-efficiency furnaces and waste forest wood (Rosillo-Calle et al., 1996). The charcoal production from trash and bagasse could benefit both the sugar and the steel industries in Brazil, but no technology has yet been developed to adapt such by-products for this purpose.