International Sugar Journal

Review of the ISSCT Co-Products Workshop

Introduction

The ISSCT Co-Products Workshop was held at the Holiday Inn Mauritius Airport from 30 November to 4 December 2015. The theme of the Workshop was Development of Co-Products from sugar mill streams and sugar cane biomass. It was organised by the ISSCT Secretariat with the support of the Mauritius Sugarcane Industry Research Institute (MSIRI) and the Omnicane Group. It was attended by 70 participants from Australia, Brazil, China, France, Germany, India, Kenya, Mauritius, Nigeria, Pakistan, South Africa, Sweden, UK, USA and Zimbabwe. At the Opening Ceremony the General Secretary of ISSCT welcomed the Honourable Mahen Kumar Seeruttun, Minister of Agro-Industry and Food Security of Mauritius who as Secretary Accountant of the MSIRI had been the Treasurer of ISSCT from 1996 when the Secretariat was created until 2005. The General Secretary also recalled the origins of the ISSCT, its objectives, its main activities namely: congresses, workshops, setting up of consortia, production of documents, etc…

The Workshop was dedicated to the memory of Mr. Maurice Paturau a Mauritian who was considered the world authority on sugar cane by-products and who had published in 1969 ‘By-Products of the sugar cane industry and introduction to their industrial utilisation’. This volume which has been published three times completely revised is considered to be the most authoritative text on sugar cane Co-Products.

The Workshop was declared open by Minister Seeruttun who in his speech welcomed the initiative of ISSCT to hold the Co-Products Workshop in Mauritius at a time of low sugar prices and the imperative need to increase revenues of producers through resorts to the entire cane biomass for the production of biofuels, bioelectricity, chemicals and bio-chemicals, bio-fertilisers, etc… diversification he stated is the order of the day.

The Keynote Address entitled Developments in biomass gasification – opportunities in the sugar cane industry’ was delivered by Dr. Lars Waldheim, Director, Waldheim Consulting, Sweden who had been involved for many many years in gasification projects of biomass including sugar cane bagasse.

The Workshop was made up of seven sessions as follows:

  1. Status of Co-Products in various countries: Australia, Mauritius, USA and Brazil.
  2. Production diversification
  3. Chemical and bio-chemical uses of Co-Products
  4. Bagasse and additional fuels
  5. Collection and uses of trash
  6. Increasing biomass
  7. Ethanol production and treatment of vinasse

Visits were made to the state-of-the-art industrial cluster of Omnicane comprising sugar factory, sugar refinery and cogeneration plant and bioethanol distillery and to Terragen where trash collection for cogeneration was demonstrated.

The final day of the Workshop was devoted to the meeting of International Sugarcane Biomass Utilization Consortium (ISBUC) which like the International Consortium for Sugarcane Biotechnology (ICSB), is an initiative of ISSCT. On its agenda were bagasse gasification, which can more than double the present energy derived from bagasse, high fibre cane, energy cane and new hybrids issuing from sugar cane and related genera like Miscanthus, Erianthus, etc… The outcome of the ISBUC meeting was the setting up of four working groups in the areas of:

  1. Trash recovery, trash quantification, storage of biomass
  2. Cane cleaning, Impact of trash on cane processing (extraction/process)
  3. High fiber cane and new cane germplasm
  4. Conversion of biomass (impact on boilers/gasification)

The technical sections were divided into specific themes and the relevant topics are highlighted below.

Product diversification

Many important sugar producing countries are looking seriously into diversification under different approaches and priorities, aiming at reducing the risk of relying strongly in one single alternative of global commodity – sugar. In South Africa, SMRI is developing a broad and detailed methodology to identify and screen co-products alternatives, comprised of several steps, in a tentative to identify the most promising ones for the South African context and market perspectives. Other countries seem to focus on advanced technology to make use of the cane residues and other crops to produce value added products such as cellulosic ethanol, chemicals, plastics, microbial oils, protein, organic acids and animal feed. In Australia the size of the national market, high costs of transport to external markets is considered as limiting factors in the choice of co-products.

In USA, a biorefinery is in the process of installation in one sugar mill in Louisiana and plans are developed to replicate the experience to other 10 sugar mills. Energy cane and sweet sorghum are under evaluation in a multiple feedstock year round processing to biofuels and biobased chemicals; intermediate products are bagasse, syrups and molasses. The final products are syrups, nanomaterials, biopolymers, biobutanol and specialty products (adhesives, epoxies and chemicals).

In the beet sugar industry diversification is already a reality in the Wissington plant in UK where the concept of maximum use of the feedstock and minimisation of wastes is carried to a full extent and several products are produced for large markets such as ethanol and animal feed and to speciality markets such as betaine and pharma/food ingredients. Other energy crops are being investigated at the Queensland University of Technology, Australia to broaden the spectrum of possible products and gains in scale, and support to commercial developments is being provided.

Chemical and biochemical uses of co-products

It is widely recognised that today’s sugar industry needs to diversify to an industry with a larger number of products. The situation of small industries exporting sugar is even more critical. Before deciding an extensive study of the alternatives is needed because they are many; just in the chemical and biochemical sector they are many with different levels of scale, prices and sophistication. The starting feedstocks are diversified also such as sugars, syrups, molasses, bagasse, trash, filter mud and can be used in a variety of way to produce a multitude of products: alcohols, amino acids, organic acids, polyols, polyphenols, nutraceutical products, animal feed, sweeteners, speciality sugars and many more. Most of the more sophisticated applications are still in the development stages, but with a high interest and potential. This is the case of aconitic acid that can be extracted from molasses or vinasse in considerable quantities, beta-glucan with its high potential use in biomedicine to control blood levels of bad cholesterol, sugars and pressure. The cane fibres can be used for energy by direct combustion or to produce special types of cellulose, pellets and charcoal briquettes.

Due to the size of the global plastic market, bioplastics are receiving a considerable amount of attention and among them the polyhydroxyalkanoates (PHAs) seems to carry a reasonable chance to become a big market product due to its similarities with major petrochemical plastics, but with the advantages of being biodegradable, renewable and GHG saving.

Cogeneration: Bagasse and additional fuels

The sugar industry in many counties has moved or is moving to cogeneration as a new source of revenues. In Australia the Racecourse mill is an outstanding example of things done right. The Racecourse cogeneration plant is fitted with 80 bar/525°C steam boiler that can burn bagasse or coal, and a condensing-extraction turbine generator set that can operate in the offseason. The surplus power sold is 25 MW with bagasse operation and 20-10 MW in peak and off-peak power conditions and operates 49 weeks per year. The plant in the Okeelanta mill in Florida, USA was designed and built by companies not familiar with fibrous fuel such as bagasse and after a series of operational problems the unit was shut down.

Poni Sugars in India has installed a high pressure cogeneration system based on a 80 t/h 110bar/535°C steam boiler and condensing extraction steam generator producing 14-14.5 MW total power and exporting 3.5-4 MW. Bagasse is depithed at the mill and the fibres sent to a paper plant and pith burned in the boiler. Several biofuels supplement the bagasse, such as sugar cane trash, coconut residues, bark, chipper dust and others. The operation with these residues deserve especial attention due to fouling, corrosion and deposit problems characteristic of agricultural residues burning.

Surplus power sale by mills in Brazil is an increasing trend and today, there are 177 mills exporting electricity to the grid from 355 mills in operation. The exported power of 19 TWh in 2014 represented 4% of the total electricity production that is far from the technical potential of 127 TWh/year due to technical and institutional problems persisting. Trash recovery in quantity and quality required for year round operation and boiler safe use is still being pursued and some regulatory barriers need to be removed to be possible to move forward at a faster pace. Electricity is sold in Brazil in two commercial environment: regulated contracting environment through government organized auctions and free contracting environment where electricity contracts are negotiated directly between generator and consumers.

Collection and use of trash

There are two ways to increase the availability of sugarcane biomass: (1) collect and use the whole cane biomass including the trash, (2) cultivate high biomass varieties bred more for energy than for sugar. Sugar cane trash represents around one third of the plant total primary energy content, however its use for different application, mostly power generation, is still incipient, In Brazil the interest to use trash has increased considerably in the past two years due to electricity price increase that resulted from the decrease in hydropower participation in the electricity matrix, due to droughts and delay in new hydro power plants conclusion.

The number of mills recovering and using trash is increasing, but there are several barriers hindering the participation of this biomass as boiler fuel. Two main collection routes have resulted from the past experiences: baling and partial cleaning system. Baling is gaining grounds due to several problems with the partial cleaning route such as high transportation costs due to decrease in density of the cane/trash load when the harvester cleaning fans speeds are reduced and the low efficiency of the cleaning stations resulting in more fiber being milled. The bailing route is suffering with the higher mineral impurity levels in the trash arriving at the mill and its consequences in the factory operation, recovery and maintenance costs.

As a tentative to identify the main problems in trash collection and use a five year project is underway conducted by the Brazilian Bioethanol Science and Technology Laboratory (CTBE), with funding from the Global Environment Facility (GEF) and co-funding from CTBE, participating mills and UNICA; the United Nations Development Programme (UNDP) manages the project for the GEF. The project objective is to increase the participation of sugarcane trash in the generation of surplus power by the mills and aims at the identification of the barriers (technical, financial, information and institutional) that are holding the increase in trash use by the mills and four mills are participating actively in the project and are being use as reference for the solution of the main problems. The sustainability analysis will be conducted to establish the criteria to define the amount of trash that needs to remain on the ground

In Mauritius the Terragen mill has started trash collection by baling, motivated by the government goal to increase the share of renewable energy in power generation to 35% by 2025. Today, bagasse accounts for 26% of the power generation.

In South Africa, a different approach is being tested at pilot scale where sugarcane is harvested green and transported to the mill with only the tops removed. A specially designed furnace burns the trash adhered to the cane, cleaning it before sending to preparation and milling. The use of the furnace heat produced is still being evaluated.

The Reunion Island is initiating a testing program with energy cane cultivated in marginal land using two different sites and 20 varieties (12 from eRcane, six from Barbados and two commercial varieties).

Increasing biomass

The interest in Mauritius to increase the renewable share of electricity and the interest of the mills to diversify even more their products has led to the study of high fibre sugarcane varieties as a way to valorise the sugarcane plant through greater utilisation of its biomass for sugar, ethanol and electricity. The sugarcane varieties were divided into four types: (1) Commercial (10-13% fibre), (2) Enhanced fibre (14-16% fibre), (3) Multi-purpose (17-20% fibre) and (4) Bioenergy (>20% fibre). In this effort, the competition with sugar production is to be avoided by trying to maintain the total sugar production per hectare at the same level of the commercial varieties and testing the bioenergy cane in two marginal land sites (very humid in the uplands and under drought conditions). An economic selection index for rapid screening of high biomass cane is being developed and the high dry matter content per hectare is being used for the initial selection phase.

In Kenya, where more than 85% of the cane is produced by small farmers the government is stimulating the diversification of products toward bioenergy applications for the sugarcane biomass in the belief that enhancing the production of renewable energy by connecting the farmers to Small Manufacturing Enterprise (SME) would enhance the farmers socio-economic standards and the sustainability of the SME’s.

Ethanol production and treatment of vinasse

The interest for diversification in the sugar industry was well explained during the Workshop and several alternatives have been explored. Based on the successful experiences in Brazil and many other countries, ethanol was presented as a low risk high volume alternative that can be applied in steps in exiting sugar mills. The feedstock can be final molasses, B molasses and juice depending on the degree of conversion of sugar to ethanol; the minimum investment and high flexibility can be achieved by annexing the new distillery to the existing sugar factory where the ratio of sugar to ethanol can be adjusted to a certain extent. Depending on the size of the markets there will be some correlation between the sugar and ethanol prices and some impact of the gasoline prices on both markets, if no subsidies are given to ethanol or sugar.

Vinasse or stillage is the main effluent of the ethanol production and can have a significant economic and environmental impact on the distillery depending on how it is disposed. The volume of vinasse produced depends on the feedstock (molasses or juice) and processing (ethanol concentration in the wine, recirculation of vinasse to the process, etc). The main treatment alternatives available are direct application, concentration to reduce volume with addition of N and P fertilizer, concentration for burning in special boilers, biodigestion with or without purification of the biogas, and composting with filter mud. The best solution will depend on the local conditions and environmental laws, size of the distillery, prices of electricity to name a few. Some of these alternatives are being used commercially and others still in the development stage. The fertilizer value of vinasse is widely recognized.

Conclusion

This Co-Products Workshop provided a platform to showcase the production and development of a range of renewable co-products derived from sugar cane and offered the opportunity for fruitful international dialogue amongst the participants from a range of countries and who had different backgrounds.

The sugarcane plant possesses exceptional photosynthetic ability which makes it the ideal candidate to be a sustainable feedstock for a large number of food and energy products.

In many countries where sugar proceeds are declining the full utilization of the sugarcane plant becomes essential in order to be profitable. The diversification of revenue streams from sugarcane includes the production of electricity and steam, ethanol (potable, industrial and fuel) and other fermentation products, fertilizers, yeasts, bioplastics, animal feed, biochemicals, etc. Advances in chemistry, biotechnology, technology and engineering are leading to new generation products which are undergoing pre-commercial testing in various laboratories around the world.

Green technologies, multiple value-added products, energy conversion efficiencies, barriers for maximum recovery, new opportunities and innovations have been at the heart of the deliberations during the Workshop, thereby fulfilling its objectives.

The advances in industrial biotechnology have made sugar a superb feedstock to produce a variety of platform chemicals via the engineered microbe route. The industry needs to look at licensing technologies developed by biotech start-ups and develop in-house expertise in this emerging sector.