Journal of Power and Energy Engineering, 2014, 2, 146-150
Published Online April 2014 in SciRes.
How to cite this paper: Montero, G., Coronado, M.A., Campbell, H.E., Cerezo, J., Lambert, A.A. and Valenzuela, E.E. (2014)
Biomass Wastes: An Energy Option for Baja California, México. Journal of Power and Energy Engineering, 2, 146-150.
Biomass Wastes: An Energy Option for Baja
California, México
Gisela Montero1, Marcos A. Coronado1, Hector E. Campbell1, Jesus Cerezo1,
Alejandro A. Lambert2, Edgar E. Valenzuela2
1Instituto de Ingenieria, Universidad Autonoma de Baja California, Mexicali, México
2Facultad de Ingenieria, Universidad Autonoma de Baja California, Mexicali, México
Received November 2013
Cotton and wheat crops are essential part of the Baja California agricultural production. Such
crops generate waste biomass after each harvest cycle, which is almost fully openly burned in or-
der to clear land for the next cycle. Thus in the agricultural 2011 cycle, 542,000 tonnes of straw
were generated from wheat in the Mexicali Valley. In addition, the residue from the cotton con-
sisting of stalks exceeded 143,000 tonnes. All these residues are a source of energy that is dis-
carded annually equivalent to 10.19 PJ. Therefore, in addition to determining the biomass poten-
tial available in the state from such wastes, the aim of this paper is to propose options for the use
of the energy contained in the waste biomass considering the characteristics of raw material
available and existing technologies. The results show that there is the potential to generate elec-
tricity with a system of 105 MW of installed capacity, and also obtain annually 6.4 million liters of
biodiesel. Obtaining this biofuel is by a transesterification reaction of waste vegetable oils, consi-
dering an average efficiency of 80% conversion, based on experimental results obtained with
mixtures from Mexicali.
Agricultural Biomass Wastes; Biodiesel; Electricity
1. Introduction
In line with the development of humanity, energy demand has increased causing the intensified use of waste as
raw material for energy production in the world, as an alternative to meet part of the demand. Also, technologies
have been developed and adapted based on the use of residual biomass, which can obtain liquid and gaseous fu-
els, heat, electricity [1]. In Mexico, biomass contributes to 3.8% of primary energy, however, in this account
only are considered sugarcane bagasse and wood and do not take into account other biomass resources from
agricultural activities, considered as waste materials [2]. Such is the case of crop residues from cotton and wheat
in the Mexicali Valley which are the main source of agricultural activities that support the regional economy.
In addition to these residues from agricultural activities in Baja California, the food preparation industry has
as remnants the Waste Vegetable Oils (WVO), which were used in cooking and are usually sent to the municipal
G. Montero et al.
sewer system, thereby causing plugging problems, odors and pollution in general.
According to the results of the project entitled: Potential and Feasibility of Using Bioethanol and Biodiesel
for Transportation in Mexico, biodiesel production from rapeseed, soybean, jatropha, sunflower, safflower,
WVO and animal tallow, the feedstocks costs represent between 59% and 91% of biodiesel production costs and
because of that, the WVO is an opportunity for biofuel production [3].
Considering these waste materials have a high energy content that can be processed for heat, electricity or fuel,
in this work it was evaluated the options to transform agricultural waste, consisting of 543,000 and 143,000 t of
wheat straw and cotton stalks respectively and 8 million liters of WVO, generated annually in Baja California by
using proven technologies [4].
2. Development
Agricultural residues, considered in this assessment and available in Baja California are wheat straw and cotton
stalks, which are generated annually after each harvest. In addition, there were the WVO generated in food
preparation establishments.
2.1. Technologies for Cellulosic Biomass Conversion
Existing technologies for converting waste biomass into biofuel, thermal energy, electric or a combination of
these, can be divided mainly into: combustion, gasification, pyrolysis and fermentation, as shown in Figure 1
Combustion is a thermo chemical process that takes place in the presence of oxygen and as a main product to
obtain thermal energy from the conversion of the chemical energy contained in the processed material. This
thermal energy is in turn used to generate steam and electricity.
Gasification involves the conversion of cellulosic biomass into synthesis gas, which can be converted into
hydrogen, methane, alcohol mixture of liquid fuel via the Fischer-Tropsch synthesis, and other chemical com-
pounds [6].
Pyrolysis is realized by thermal decomposition of biomass in the absence of oxygen. Depending on operating
conditions may be obtained the so-called bio-oil or pyrolysis oil, synthesis gas (H2 and CO), tars and charcoal.
Pyrolysis oil can be converted into diesel by hydrotreating and hydrocracking processes and to modify their
properties so that it more suitable for use as a liquid fuel.
In fermentation a biochemical conversion is performed, i.e involving microorganisms such as yeasts aimed at
Figure 1. Technologies for cellulosic biomass conversion.
G. Montero et al.
converting organic matter into ethanol.
This process achieves the conversion of 50% to 60% of the feed stream and the remainder is a byproduct,
which can be used as compost. In the case of cellulose, a pretreatment is necessary for hydrolysis to convert it
into sugars that are subsequently fermented.
2.2. Technologies for Vegetable Oil Conversion to Biodiesel
The American Standard for Testing and Materials (ASTM) defines biodiesel as a mixture of mono- alkyl esters
of long chain fatty acids, derived from vegetable oils or animal fats, and are used in compression - ignition en-
gines. The processes for obtaining such esters differ essentially in the type of catalyst used and are named: acid
catalyst, base catalyst , or a mixture of both and enzymatic catalyst, which are described below.
Alkaline catalyst. Is commonly used sodium hydroxide or potassium hydroxide with a short chain alcohol
such as methanol or ethanol, as well as any type of vegetable oil. It is recommended to prepare the alkoxide in
order to obtain a better overall efficiency of the reaction. Alkaline catalysed process is performed faster than the
process with acid catalyst. Typical temperatures at which this reaction is performed is 60˚C and is complete in
about 1 hour.
Acid catalyst. In this method sulfuric or sulfonic acid is used, which catalyzes the reaction between the raw
material composed of fatty acids and triglycerides (oil or fat) and methanol. In both types of catalysts, an excess
of alcohol improves the conversion efficiency of triglycerides but glycerol recovery is more difficult. The typi-
cal reaction temperature is above 100˚C and requires more than 3 hours for complete conversion.
Enzymatic catalyst. Catalysts used allow the transesterification of triglycerides, both in aqueous and
non-aqueous systems. In this catalytic route, the free fatty acids present in the fat and WVO can be converted
completely into alkyl esters. This represents an advantage over previous procedures. However, production costs
in this way are greater than those for alkaline and acid catalyst [7].
Transesterification process. Glycerol is replaced by a simple alcohol such as methanol or ethanol, so as to
produce methyl or ethyl esters of fatty acids.
The transesterification reaction can be represented as follows [8]:
12 21
trygliceride + alcohol est er + glycerol
where in a simplified way: R = fatty acid chain; R1 = triglyceride chain and R2 = methyl or ethyl group.
2.3. Biomass Resources in Baja California
In 2011, the residue from the cotton cultivation in the Mexicali Valley, comprised by cotton stalks exceeded
143,000 t [9,10]. This was calculated considering a planted area of 32,461 ha, generation index of cotton stalks
at 4.42 ton/ha [11] and a lower heat value (LHV) equal to 14.79 MJ/kg [12].
The wheat crop in 2011, reached 74,260 ha, with a rate of generation of straw at 7.3 t/ha [13]. It was consi-
dered a LHV of 17.5 MJ/kg [14] and that 85% of the straw generated in each agricultural cycle is burned in situ
[15]. In relation to the WVO, and as a result of a research project of the Institute of Engineering, which was de-
veloped in an exploratory study, it was possible to make an estimate WVO generation of the Mexicali restaurant
sector, which in 2010 totaled approximately 8 million liters per year [4]. Experiments were conducted using dif-
ferent samples of WVO and on average, 0.8 liters of biodiesel obtained per liter of WVO via alkaline
3. Results and Discussions
3.1. Energy Content of Waste Materials
Figure 2 summarizes the results of the energy content of waste materials. The wheat straw and cotton stalks,
show an energy balance of 10,105 TJ. While the WVO is potentially recoverable an annual amount of 206 TJ.
3.2. Optional Uses for Biomass Resources of Baja California
There are several commercially available technologies for the conversion of biomass through direct combustion
G. Montero et al.
Figure 2. Energy potential of agricultural bio-
mass waste.
for electricity generation. In the pyrolysis and gasification unlike direct combustion, biomass is raw material to
produce a more valuable fuel (or heating power) which can be subsequently used in more specialized equipment
and more efficient as called CHP (combustion heat and power).
These technologies converting biomass into higher value-added energy, involve higher cost of investment,
operation and skilled labor. However, it is noteworthy that both technologies are capable of processing a wide
variety of materials classified as waste, including hazardous.
For the generation of electricity by direct combustion of biomass is estimated that the best option is to distri-
bute small independent modules. Also, it is highly recommended that the plant was constructed as close to the
generation of biomass for avoiding transportation costs.
The fermentation was not considered as a relevant choice for this type of material because the lignocellulosic
material must be previously hydrolyzed to convert sugars and then fermenting. However, such hydrolysis is
complicated to put it into practice due to acidic media handling affecting performance of the bacteria used in the
In relation to production costs, the reported values are from 3.8 to 10.2 c/kWh (U.S.) for a system whose
technology is pyrolysis processing energy crops; 7.8 c/kWh (U.S.) for a gasifier is fed with low-cost plantations;
12.7 c/kWh (EU) for power generation by direct combustion of agricultural residues and 9.3 to 12.4 c/kWh
(U.S.) for the case of electricity generation from straw combustion [16].
4. Conclusions
Considering the waste generated annually, Baja California can replace a significant fraction of fossil fuel con-
sumption by using the energy contained in the waste biomass. This would increase the renewable energy share
in the energy of Mexico.
The production of electricity from biomass is a competitive option compared to wind generation from the
plant located in La Rumorosa. Besides agricultural residues considered in this assessment, it is advisable to in-
clude materials generated by other crops typical of Baja California. It is also very important that in addition to
oleic wastes from restaurants be accounted for WVO generated at the household level and to contemplate alter-
natives for processing waste such as plastics, tires and hazardous waste generated in hospitals, which can be
transformed materials with high added value and high energy through processes such as pyrolysis and gasifica-
G. Montero et al.
The authors thank to the Universidad Autonoma de Baja California for its support to develop this research.
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