EXPERIENCES ON VINASSE DISPOSAL: Part III: COMBUSTION OF VINASSE-# 6 FUEL OIL EMULSIONS

EXPERIENCES ON VINASSE DISPOSAL

Part III: COMBUSTION OF VINASSE-# 6 FUEL OIL EMULSIONS

L.A.B. CORTEZ¹ and L.E. BROSSARD PÉREZ2

¹Faculty of Agricultural Engineering - State University of Campinas - CEP 13081-970 - Campinas, SP - Brazil

E-mail: [e-mail] - Phone: [phone] - Fax: [phone]

²Faculty of Chemical Engineering - Oriente University, Santiago de Cuba, Cuba

(Received: July 1, 1996; Accepted:January 4, 1997)

Abstract - Vinasse, a residual substance left after sugarcane alcohol distillation, represents a major environmental problem for the ethanol industry. No one has found a convenient and economical disposal solution for this black-reddish (Vinasse presents a light brown color and a low total solids content, from 2-4%, when it is obtained from straight sugarcane juice and a black-reddish color and total solids ranging from 5-10% when it is obtained from sugarcane molasses, which is the case of the vinasse used in this study.), viscous, high B.O.D. and acid material which is produced in quantities up to 15 times larger than those of the alcohol itself. This research investigated and developed the basic technology of on-site disposal of vinasse by combustion. Besides the clean ecological benefit, this method promotes energy savings and extra benefits when rich potassium vinasse ash is commercialized. Basic research was conducted using the facilities in the Combustion Laboratory (Mechanical Engineering Dept. at the Louisiana State University Campus in Baton Rouge). This research on vinasse combustion consisted of determining heating values, composition, and flame characteristics through combustion tests. Initially only vinasse was used in different solid concentrations and later emulsions were prepared using vinasse and # 6 fuel oil.

Keywords: Vinasse disposal, combustion, fuel oil emulsions.

INTRODUCTION

The disposal of vinasse, the major effluent from the ethanol industry, represents a major environmental problem. This black liquid that is produced at a rate 10 to 15 times greater than the ethanol itself is a mixture of water and organic and inorganic compounds. These compounds remain after different steps involving the sugar cane production and processing. These hazardous substances cause the vinasse to have a very high B.O.D. (Biological Oxygen Demand), ranging from 30-40,000 and presenting a pH of 4-5 (Polack et al., 1981).

Research has demonstrated that vinasse disposal in river basins alone isn’t a convenient disposal solution. Due to its high B.O.D., this material can cause damage to aquatic life, especially when dumped in large volumes. In Brazil, most of the vinasse that results from ethanol production is being used as fertilizer due to its high potassium content (Glória, 1975). The problem occurs when some soils don't respond positively to the application of this acid material. The disposal problem is aggravated by an economic drawback, because water must be evaporated for easy transportation at low costs.

Some other applications, like methane gas production by anaerobic fermentation, have been investigated but the economics associated with technical problems acts as a limiting factor. This paper investigates the technical feasibility of on-site vinasse disposal via combustion. Preliminary evaluations of heating values, and determinations of composition encouraged the investigation of its potential to sustain combustion. The results verify what was reported by Polack et al. (1981). Finally, a series of combustion tests demonstrated that vinasse mixed with # 6 fuel oil would be an appropriate way to dispose of the waste material by combustion.

A BRIEF HISTORY OF VINASSE COMBUSTION

The combustion of vinasse has been investigated by several researchers, who achieved varying results. According to Kujala et al. (1976), the concept of vinasse evaporation followed by combustion dates back to World War I, when the Porion Furnace was developed by Whitaker and U.S. Industrial Chemicals Inc. In addition, Reich (1945) proposed a concentration of vinasse in a

quadruple effect evaporator up to 70-80% solids, followed by subsequent combustion (343° C) using the resulting carbon to produce potash and ash char. The same principle was used in Lucknow, India by Chakrabarty (1964) in the distillery of the Dyer Meaking Breweries Ltd., when a pilot plant was built for the recovery of potassium salts from molasses alcohol stillage (M.A.S.). Two incineration plants were installed in Brazil in the state of Pernambuco around 50 years ago but both were closed after a short time for economic reasons (D'Andrada cited in Monteiro, 1975).

Although most of the existing literature reports success when incineration is used as a disposal method, lack of information prevents this technology from being applied to solve the stillage problem. Gupta et al. (1968) was perhaps the first to conduct experiments using a fluidized bed combustion unit. The vinasse was prepared at 30-40° BRIX and then spray dried and combusted at 700° C. A similar scheme was described by Dubey (1974) who used a dual fuel furnace (vinasse at 60% solids and bagasse). According to Sheehan and Greenfield (1980), Yamauchi and collaborators in 1977 also conducted experiments on the combustion of vinasse at a 21% solids concentration with heavy oil. Here, the flue gas was used as the heat source and the ash as a fertilizer. More recently, a Dutch company named Hollandse Constructive Group B.V. reported (H.C.G. 1980; Spruytenburg, 1982) the complete combustion of vinasse with a concentration up to 60% solids in its specially designed steam generator. The Swedish Alpha-Laval (Nilsson, 1981) also reports the technical, economic, and commercial feasibility of burning vinasse. Both reports mention the use of "swirl" combustion technology to burn 60% solids vinasse. However, none of the above mentioned papers report detailed technical information regarding the combustion of vinasse itself.

Polack et al. (1981) showed that Louisiana's vinasse is a very difficult effluent to be disposed via incineration, and research conducted did not lead to any technical development in this area. The authors used a modified bagasse furnace previously developed by Harper (1980) which was adapted and equipped with an air atomizing burner (Eclipse Convecto-Flame oil burner Model 168 HCF-CGO) and fed at pressures of 51 cm of H₂O to 1.4 kgf/cm² (1.4 MPa). The furnace firebox was maintained at from 760 to 927° C by firing with natural gas and the pre-heated (50° C) vinasse was atomized in concentrations varying from 63.9 to 73° BRIX. Because Polack had not been successful in the combustion of vinasse, even after experimenting different alternatives such as the use of pre-heated air and different air/fuel ratios, reporting no flame and no sustainable combustion, the present research was initiated using vinasse-oil fuel emulsions as a possible alternative fuel.

BASIC COMBUSTION STUDIES

Initially, due to the absence of information about vinasse, a significant amount of laboratory work had to be conducted to determine Sherpherd Oil Distillery's molasses vinasse composition. Table 1 presents vinasse composition evaluated in different countries and sources. It can be noted that the results vary considerably, because vinasse composition can be affected by several parameters. These property differences are caused by sugarcane production and the industrial processing of the ethanol itself. Table 2 presents the vinasse composition in the perspective of its use as a fuel (as received and dry basis), Table 3 presents a comparison between vinasse, sugarcane bagasse, and coal as far as ultimate analysis is concerned and Table 4 shows some typical heating values for sugarcane products, such as alcohol, and by-products, such as bagasse and vinasse. Particular attention should be given to the material's proximate analysis which gives the percent of volatile matter and fixed carbon used as fuel. These values indicate that vinasse has a substantial potential application as a boiler fuel.

The heating values of vinasse-oil fuel emulsions are given by equation 1, which was developed using 45° BRIX molasses vinasse with a heating value of 7,800 kJ/kg (Kujala, 1979) and # 6 fuel oil with an average heating value of 43,350 kJ/kg (ASHRAE Fundamentals Handbook, 1993). Also, a good correlation was obtained with the previously reported heating values (Kujala, 1979) of 6,187 BTU/lb (14,390 kJ/kg) dry basis for vinasse only and heating values experimentally determined using Shepherd Oil Distillery's molasses vinasse (equation 1). In this determination, PARR Adiabatic Calorimeter Model 1241 was used. The vinasse was evaporated and samples with solids concentrations varying from 10 to 73% were submitted for the rheological studies (see Experiences on Vinasse Disposal, Part II), and from 40 to 100% solids for the combustion

experiments. In the bomb calorimeter experiments, combustion was observed only in vinasse concentrations above 70%. The goal of this study was to determine the properties that would allow atomization which is required for successful combustion to be accomplished.

(1)

where:

is the low heating value for the vinasse-# 6 fuel oil emulsions in kJ/kg

7,800 kJ/kg is the heating value of 45° BRIX molasses vinasse

X is the vinasse fraction in the vinasse-# 6 fuel oil emulsion

43,350 kJ/kg is the average heating value of # 6 fuel oil

Y is the # 6 fuel oil fraction in the vinasse-# 6 fuel oil emulsion

Because previous research has revealed that # 6 fuel oil should be added to the vinasse for combustion, a number of tests were performed to evaluate the heating values of # 6 fuel oil-vinasse emulsions.

Another important combustion parameter is the adiabatic or theoretical flame temperature. This composition dependent parameter was calculated using the same Shepherd Oil Distillery vinasse which had its composition analyzed by the Guardian laboratories. Based on dried composition and different water contents (Table 2) and the heating value (Table 4), the vinasse approximative formula can be calculated (C_0.0331 H_0.0860 N_0.0012 O_0.0194) and based on that vinasse’s moleculecular weight (13.431 kg). Than, for the air/fuel ratio is 7.621 kg of air/kg of fuel (on dry-ash free basis), the main results for the adiabatic flame temperatures are 1290° F (700° C) for 50% solids and 1460° F (793° C) for 60% solids vinasse.

Vinasse Origin Source Composition, wt % Total Solids % Organic Solids % pH K P N Ca Mg Ash Brazil (1) Brazil (2) Australia (1) Australia (2) India Louisiana (*) Molasses Juice Molasses Molasses Molasses Molasses 0.48 0.17 0.86 1.05 0.4-1.2 0.89 0.01 0.007 0.002 0.012 0.5-1.5 0.0001 0.04 0.01 0.31 0.18 0.1-0.12 0.015 0.07 0.04 0.11 0.2 n.a. 0.014 0.02 0.01 0.15 0.13 n.a. 0.006 1.95 1.5 3.2 n.a. n.a. 5.0 46.47 6.69 n.a. 9.0 6-8 n.a. 4.63 5.14 n.a. n.a. n.a. n.a. 4.8 4.6 n.a n.a. 4.3-5.3 4.5

Vinasse Origin	Source	Composition, wt %						Total Solids %	Organic Solids %	pH
		K	P	N	Ca	Mg	Ash
Brazil (1) Brazil (2) Australia (1) Australia (2) India Louisiana (*)	Molasses Juice Molasses Molasses Molasses Molasses	0.48 0.17 0.86 1.05 0.4-1.2 0.89	0.01 0.007 0.002 0.012 0.5-1.5 0.0001	0.04 0.01 0.31 0.18 0.1-0.12 0.015	0.07 0.04 0.11 0.2 n.a. 0.014	0.02 0.01 0.15 0.13 n.a. 0.006	1.95 1.5 3.2 n.a. n.a. 5.0	46.47 6.69 n.a. 9.0 6-8 n.a.	4.63 5.14 n.a. n.a. n.a. n.a.	4.8 4.6 n.a n.a. 4.3-5.3 4.5

Table 1: Comparative vinasse composition from different countries and sources*

(*) this analysis was conducted at the Feed and Fertilizer Laboratory at L.S.U. using Shepherd Oil Distillery vinasse.

Source: remaining data extracted from Polack et al., 1981

As Received Dry Basis Solids, % Ash, % Sulphur, % 29.79 13.31 0.08 n.a. 18.95 0.12 Volatile Matter, % Fixed Carbon, % 48.67 8.24 69.31 11.73 Carbon, % Hydrogen, % Nitrogen, % n.a. n.a. n.a. 39.72 8.60 1.65

	As Received	Dry Basis
Solids, % Ash, % Sulphur, %	29.79 13.31 0.08	n.a. 18.95 0.12
Volatile Matter, % Fixed Carbon, %	48.67 8.24	69.31 11.73
Carbon, % Hydrogen, % Nitrogen, %	n.a. n.a. n.a.	39.72 8.60 1.65

Table 2: Shepherd Oil Distillery vinasse "as received" and "dry basis" composition

Analysis Vinasse*1 Bagasse*2 Coal*3 Proximate Ultimate Fixed Carbon, % Volatile Matter, % C, % H, % O, % S, % N, % Ash, % Moisture, % 39.72 69.31 39.72 8.60 n.a. 0.12 1.65 18.95 » 0 6.1 40.2 23.8 2.8 20.1 trace trace 1.7 52.0 16-93 3-50 50-95 2-5.5 2-40 0.5-7 0.5-3 2-30 » 0

Analysis		Vinasse*1	Bagasse*2	Coal*3
Proximate Ultimate	Fixed Carbon, % Volatile Matter, % C, % H, % O, % S, % N, % Ash, % Moisture, %	39.72 69.31 39.72 8.60 n.a. 0.12 1.65 18.95 » 0	6.1 40.2 23.8 2.8 20.1 trace trace 1.7 52.0	16-93 3-50 50-95 2-5.5 2-40 0.5-7 0.5-3 2-30 » 0

Table 3: Comparison of ultimate and proximate analyses between vinasse, sugarcane bagasse, and coal

Sources: *1 analysis made using Shepherd Oil Distillery vinasse; *2 Harper (1980); *3 Haalam and Russel (1926)

Product/By-Product Heating Value, kJ/kg Ethanol (96%)*1 Bagasse dry*2 Bagasse 60% dry solids*2 Vinasse dry*3 Vinasse 60% dry solids*3 27,837 18,600-20,935 10,410 12,560-15,070 7,600

Product/By-Product	Heating Value, kJ/kg
Ethanol (96%)*1 Bagasse dry*2 Bagasse 60% dry solids*2 Vinasse dry*3 Vinasse 60% dry solids*3	27,837 18,600-20,935 10,410 12,560-15,070 7,600

Table 4: Typical heating values of sugarcane products and by-products

Sources: *¹ MME (1994); *² Harper (1981) *³ Polack et al. (1981)

COMBUSTION TESTS

The core of this research was conducted in the Combustion Laboratory located in the Mechanical Engineering Department at Louisiana State University. This laboratory is a complete combustion facility that allows conduction of combustion experiments of this nature.

The combustion chamber is a refractory lined surface with no boiler-type heat transfer surfaces present. It has inner dimensions of 5 ft (1.52 m) wide x 5 ft (1.52 m) high x 10.75 ft (3.28 m) long, giving an inner volume of 269 cubic feet (7.62 m³). Overall outer dimensions are 8 ft (2.44 m) wide x 7 ft (2.13 m) high x 12 ft (3.66 m) long, as shown in Figure 1. The furnace is equipped with a complete cooling system to provide safe operation. It also has a view port in the rear wall that provides visual observation of the flame and also allows photographs to be taken of the flame. The furnace temperature is measured by the thermocouples installed inside the furnace (Figure 2 gives location). These thermocouples are recorded by a Datalogger System allowing data recording.

The fuel feeding system is shown in Figure 3. It consists of two storage barrels, a pump, and a piping system to supply the fuel to the furnace. The barrels are equipped with an independent heating system to supply the fuel to the furnace. The barrels are equipped with independent heating systems that control fuel temperature. The fuel is atomized in the hot furnace (more than 1500° F and heated with natural gas) by the burner shown in Figure 4. The fuel is surrounded by an air jet that breaks the fuel into small particles, allowing contact between the combustion air and the droplets. Pictures of the flame were taken for each test conducted.

The combustion experiments were performed, varying the emulsion vinasse and # 6 fuel oil proportions and always using 45° BRIX. First, pure # 6 fuel oil was burned at 50 lbf/in² (0.34 MPa) and combustion parameters were set for further comparison. Then, combustion tests were conducted increasing vinasse proportions in the emulsions: 10, 12.5, 15, 25, 40, and 50%. Tests with diesel-vinasse emulsions were not conducted because of difficulties to sustain stable emulsion once they were heated.

Results from combustion tests are presented in Figure 5. Excess air in the stack was varied and Carbon Monoxide (CO) and Oxygen (O₂) were measured. The results presented show that there is a clear tendency to stabilize the CO content in the flue gas when the proportion of vinasse in the mixture is raised.

They suggest that the effect of O₂ in diminishing CO concentration in the flue gas works well with 100% # 6 fuel oil but does not operate in the same way when # 6 fuel oil-vinasse emulsions are burned instead.

In the last case, emulsions with 20% vinasse and higher reach an almost constant CO content in the flue gas of 105 to 110 ppm independent of the presence of O₂. This means that the introduction of vinasse makes the complete combustion of # 6 fuel oil more difficult, probably because of the oil-in-water type of emulsion that is formed when both components are thoroughly mixed.

The presence of an increasing proportion of a non-combustible continuous phase (mainly water) that surrounds the oil droplets in the emulsion, should be an obstacle for O₂ access resulting in poorer combustion. In this way an increase in O₂ in the burning emulsions works well up to a certain limit that depends on the proportion of water in the particular emulsion. When the water content is high enough (i.e., 20%) a constant CO content in the flue gas is reached as O₂ - # 6 fuel oil contact in the emulsion is not further improved.

Figure 1: The Combustion Chamber Dimensions and Main Components.

Figure 2: Thermocouple Location Inside the Combustion Chamber.

Figure 3: The Fuel Feeding System Used During the Combustion Experiments.

Figure 4: Front and Cross-Section View of the Burner Used During the Combustion Experiments.

Figure 5: Flue Gas Composition for Different # 6 Fuel Oil-Vinasse Mixtures.

CONCLUSIONS

Because the purpose of this research was to generate enough data to evaluate the technical feasibility of vinasse combustion via atomization, the conclusions can be derived from two different perspectives: a) Rheological; and b) Combustion.

a) Rheological: Both the vinasse alone and the # 6 fuel oil-vinasse emulsions have rheological behavior close to the # 6 fuel oil alone when they are submitted to about 200° F (90° C) in the Brookfield Rotary Viscometer. Once the correct temperature and shear rate were obtained, atomization and combustion problems did not occur during any of the tests. Vinasse solids concentration below 50% was used for the combustion tests conducted.

b) Combustion: The combustion of # 6 fuel oil-vinasse emulsions is feasible in the range of 95% # 6 fuel oil-5% vinasse to 50% # 6 fuel oil-50% vinasse emulsions. Although emulsions with more than 50% vinasse have a satisfactory heating value, the resulting flame was unstable and not compact. Although the vinasse concentration was tested over the wide range given above, the best results were obtained with 95 to 75% # 6 fuel oil-5 to 25% vinasse.

Among the existing drawbacks of vinasse combustion, the following can be pointed out:

a) The considerable amount of energy used during vinasse pre-evaporation, which is a process required for combustion;

b) The foaming in the evaporators when concentrating up to 75% solids;

c) The salt crystallization in the syrup, causing pumping difficulties;

d) The ash fusion occuring at 700° C, thus limiting the incineration operation. Melted ash creating insoluble solids with no commercial value;

e) The difficult task of recovering salts and technology still under development.

f) Additional studies on the vinasse atomization patterns are necessary because of this parameter affecting the combustion efficiency. The atomization is, naturally, a function of vinasse solids concentration, temperature, nozzle type, vinasse and air pressures and temperatures, among other important factors.

ACKNOWLEDGMENTS

The authors thank the Brazilian National Council for Scientific and Technological Development-CNPq and the State of São Paulo Research Foundation-FAPESP for the financial support which made this research possible.

REFERENCES

ASHRAE, 1993 ASHRAE handbook Fundamentals, chapter 15, pp.15.6, Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (1993).

Chakrabarty, R.N., Potash Recovery - A Method of Disposal of Distillery Wastes and Saving Foreign Exchange, Symposium on Ethyl Alcohol Production Technique, New Delhi, India, pp. 93-97, Publ. Noyes Development Corp., N.Y., U.S.A. (1964).

Dubey, R.S., Distillery Effluents-Treatment and Disposal, Sugar News Ann. Number 6, pp. 9-26 (1974).

Glória, N.A. da, Utilização Agrícola da Vinhaça (in Portuguese), Brasil Açucareiro, November, vol. 86, pp. 11-17 (1975).

Gupta, S.C.; Shula, J.P. and Shukla, N.P., Recovery of Crude Potassium Salts from Spent Wash of Molasses Distilleries by Fluidized Incineration, 1968-Proceedings of the 36th Annual Conv. Sugar Technology Ass., India, XXXXIII-1 to XXXXIII-7 (1968).

Haalam, R.T. and Russel, R.P., Fuels and Their Combustion, McGraw Hill Co., New York, N.Y., pp. 809 (1926).

Harper, G.L., Combustion System Development for Firing of Pulverized Bagasse, M.Sc. Thesis, Mechanical Eng. Dept., Louisiana State University, Baton Rouge, La, USA, December (1980).

Hollandse Constructie Groep B.V., Energy Saver-NEM Vinasse Fired Boiler, (Advertisement), International Sugar Journal, LXXXII, 978, June (1980).

Kujala, P., Distillery Fuel Savings by Efficient Molasses Processing and Stillage Utilization, Sugar y Azucar, October, pp. 13-16 (1979).

Kujala, P.; Hull, R.; Engstrom, F. and Jackman, E., Alcohol from Molasses as a Possible Fuel and Economics of Distillery Effluent Treatment, Sugar y Azucar, March, vol. 71, pp. 28-39 (1976).

MME, Balanço Energético Nacional-1994, Ministério das Minas e Energia, Brazilian Gouvernment Publication, Brasília, D.F., Brazil, p. 140 (1994).

Monteiro, C.E., Brazilian Experience with the Disposal of Waste Water from the Cane Sugar and Alcohol Industry, Process Biochemistry, November, pp. 33-41 (1975).

Nilsson, M., Energy Recovery from Distillery Wastes, from Alfa-Laval A.B., International Sugar Journal, September, vol. 83, issue 993, pp. 259-261 (1981).

Polack, J.A.; Day, D.F. and Cho, Y.K., Gasohol from Sugarcane-Stillage Disposition, Audubon Sugar Institute, Louisiana State University, September, p. 47, (1981).

Reich, G.T., Production of Carbon and Potash from Molasses Distillers' Stillage, Trans. Amer. Inst. Chem. Engrs., 41, pp. 233-251 (1945).

Sheehan, G.J. and P.F. Greenfield, Utilisation, Treatment and Disposal of Distillery Wastewater, Water Research, Vol. 14, pp. 257-277, Great Britain (1980).

Spruytenburg, G.P., Vinasse Pollution Elimination and Energy Recovery, from Hollandse

Constructie Groep B.V., International Sugar Journal, March, pp.73-74 (1982).

Publication Dates

• Publication in this collection
  06 Oct 1998
• Date of issue
  Mar 1997

History

• Accepted
  04 Jan 1997
• Received
  01 July 1996