Biomass and self-consumption: a viable alternative for the food industry

Self-consumption with biomass

An installation to generate electricity from biomass whose power is less than 1 MWe is likely to be included in the so-called "self-consumption", extending its scope to other sectors such as industry, for example.

Introduction. Regulatory framework

When talking about self-consumption in Spain, everyone thinks directly about photovoltaic solar technology and a building. The reason? It is possibly the only thing that is spoken when the term "self-consumption" appears in the media.

However, according to the Royal Decree 1699 / 2011, of November 18, which regulates the connection to the network of small power electric power production facilities (BOE number 295 of 8 of December of 2011) in its article 2 "scope of application" states the following: "it will also apply to installations of ordinary regime and special regime of power not exceeding 1.000 kW of the technologies contemplated in category a) and subgroups b.6, b .7 and b.8 of the article 2 of the Royal Decree 661 / 2007, of 25 of May, that are connected to the lines of tension not superior to 36 kV of the distributing company, either directly or through an internal network of a consumer . "

Category a) and the mentioned subgroups correspond to the following technologies: cogeneration or other forms of electricity production from residual energies and different types of biomass.

Therefore, an installation for generating electricity from biomass whose power is less than 1 MWe is likely to be included in the so-called "self-consumption", also extending its scope to other sectors such as industrial, for example. In the image a photo of orujillo, a biomass abundant in Andalusia and with some extraordinary properties for its thermochemical conversion.

Types of self-consumption. Project type

Two categories or groups are established, the so-called Type 1 and Type 2. The first is applicable to supplies with contracted power lower than 100 kW, and the second allows power generation up to the limit of the power contracted with the limitation of 1 MWe. The main characteristics of this group are the following:

1. Generating power ≤ Contracted power
2. Obligation to process the connection with the distribution company, even if the discharge to the network is not foreseen.
3. Need to register the installation in the self-consumption and generation records.
4. The energy discharged to the grid may be marketed under current legislation.
5. The owner of the installation is subject to the so-called tolls.

Therefore, an installation for generating electricity from biomass carried out in an industry with an electrical power lower than 1 MWe, would be considered Type 2, provided that it was lower than the one contracted by it.

For example, a typical project could be the following:

• Agro-food industry or forestry sector that generates lignocellulosic residual biomass in its production process (chips, orujillo, ...). Group b.7. RD 661 / 2007.
• Contracted power ≤ 1 MWe.
• Thermal requirements for process (drying, evaporation, hot water, ...) and / or heating (hot water).
• Annual operation ≥ 7-8 months / year.

Now, the technology of energy valorization of biomass in this case would be gasification, which would be part of a thermoelectric cogeneration installation for the combined production of heat and electricity. This is due to its gas versatility as fuel for use in thermal machines such as engines or turbines.

• Modularity, that is, can be based on powers of the order of 100-150 kWe.
• The facilities for the installation in the industry itself and for the evacuation of the surplus electric power generated, due to the fact that these are not very high powers.
• The low-average consumption of biomass in relation to traditional biomass plants, which reduces the risks.
• High energy efficiency, taking advantage of the residual thermal energy from the cooling and exhaust of the engines, being able to reach values ​​of the order of 70-75%.

In a generic scheme, applicable to an agri-food industry or the forestry sector, it could be seen that from residual biomass a series of flows are generated, which allow obtaining savings or new revenues for the industry from which to amortize the investment. In this example, three solutions are integrated:

1. The production of standardized solid biofuels for thermal generation.
2. The self-production of electrical and thermal energy through gasification.
3. Obtaining water suitable for irrigation.

The anaerobic digestion would be another technology that could be compatible with the binomial autoconsumo-biomass, although applied to other types with greater degree of humidity and a more residual character as for example the muds of EDAR or the purines of pig, among others.

Biomass gasification technology

Gasification is a thermochemical conversion process widely used in the field of biomass, although it is not widespread in Spain. It consists of an incomplete combustion that occurs when the biomass is subjected to a temperature of about 1.000 ° C in a low oxygen atmosphere. The resulting product is a synthetic gas (syngas or synthesis gas, formerly gas gas) which consists basically of CO (35-40%), CO2 (25- 35%), H2 (20-40%), CH4 ( 0-15%), hydrocarbons and H2 O and that can be used for thermal and / or electrical purposes. Its average PCI is approximately 1.050 kcal / Nm3.

A waste biomass gasification plant is formed by the following main elements:

• System for feeding biomass to the gasifier. The two requirements to consider are the humidity, which has to be below the 20%, and the granulometry, which must be homogeneous.
• Gasifier. In this case it is "down draft" type or parallel currents because it allows to obtain a gas with a lower tar content, which facilitates the subsequent cleaning processes. There are also others such as "up draft" or counter current, fluid bed or plasma.
• Syngas cleaning and treatment system generated. Composed by filters of different nature, condensers, chillers, etc.
• Motor generator group.

The viability of the project

A project of these characteristics must be viable in economic terms, recovering the investment in a reasonable period of time (5-7 years) and obtaining an attractive return for the investor (TIR »10-12%).

The main parameters that will condition the above and on what will have to act are the following:

• Total investment: engineering, equipment, civil works, electrical connection, ...
• Supply (t / a), characteristics (humidity and granulometry) and cost of biomass (€ / t).
• Operation and maintenance costs (€ / a). Tolls (€ / a).
• Electricity saving (€ / a).
• Income from the sale of electricity (€ / a).
• Use of heat (€ / a).

It could be applicable to industries in the olive oil and pomace oil sector, such as mills and extractors, industries in the forestry sector such as pellet factories, etc. In addition, with the added advantage of being able to use the gas not only to be introduced in an engine or turbine, but also, once filtered, to use it in a boiler or combustion chamber in drying processes with the consequent reduction of emissions to the atmosphere in terms of particles.

This aspect is very positive for the thermal generation with biomass since the levels of emission of particles to the atmosphere are being analyzed and a reduction of them to levels below 150 mg / Nm3 is imminent.

Conclusions

Self-consumption can be a viable alternative for certain industries that generate residual biomass and demand for electrical and thermal energy, because it will allow them to reduce their energy costs and obtain other indirect benefits such as reducing emissions to the atmosphere, not just those of CO2 but also others like those of particles.

In the development of self-consumption as a technically viable option it will be necessary to solve pitfalls, among others, such as evacuation points or famous tolls, something of which there is little experience in Spain and of which it has been talking for some time that they are going to be eliminated , which will undoubtedly contribute to improving the profitability of this type of investment.

Article extracted from the energetic magazine, nº 179 September 2018. Author: José Antonio La Cal Herrera DR. Industrial Engineer. Founding partner of BIOLIZA SPIN OFF of the University of Jaén.
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