The integration of a MSW plasma gasification plant in a Smart Grid in Andújar (Jaén)

Ignacio Romero Gómez ICAI School of Engineering

Comillas Pontifical University Madrid, Spain

nacho.romero.gomez@gmail.com

Abstract— The organic part of the MSW is an important biomass resource, which has not properly used to satisfy the energy demand yet. The objective of this project is to set out a smart grid using local renewable resources, in which the plasma gasification of MSW is the main contributor. This smart grid seeks to increase the system efficiency, to reduce operational cost and to optimize the distributed power generation, reducing the external dependency.

Keywords- Smart grids; plasma gasification; municipal solid waste (MSW); fuel cells.

I. INTRODUCTION

The case study has been carried out in Andújar (Jaén), South of Spain, with an average population of 39.500 inhabitants. In the surroundings there are photovoltaic, biomass coming from the olive oil production and mini-hydraulic power plants; all these current plants will also be parts of the smart grid.

A micro-grid is a low voltage network that interconnects a group of energy resources close to each other; including the generation, the storage and the final consumption. Micro-grids usually work independently from the main transport network. When the local generation cannot supply the local demand, the micro-grid takes power from the main network; and the same in the other way, if the local generation is higher than the demand, the oversupply will be delivered to the main network.

The main problems, that the Spanish power system has to face, are:

System inefficiency due to transportation lost energy around 8% and too high operational costs.

The energy dependency ratio is close to 80%, and it is superior to the average European ratio.

Bad implementation of the distributed power generation that causes technical and economic problems, so it requires a suitable network system.

Furthermore these problems make even worse because of an inappropriate power development plan, where sources with less or none manageability have received financial aids before other sources. Power installations, like photovoltaic or wind power, require a high investment for the technology itself and for the necessity of back-up power installations; so these energies are not very competitive. Meanwhile, other interesting and potential sources in Spain have not been considered in the same way.

Therefore, the incentive for this project is to offer a real solution to the existing problems in the Spanish power system. In particular, the case that is being analyzed is the residential center of Andújar (Jaén). In order to achieve this objective, this project set out the integration of a micro-grid with local and manageable resources that increase the system efficiency, reduce operational cost, optimize the distributed power generation, reduce the external dependency and go towards a sustainable future.

In order to analyze properly this case and attempt to find a real solution to these problems, the research will be divided in five sections.

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International Conference on Renewable Energy Research and Applications Madrid, Spain, 20-23 October 2013

ICRERA 2013 617

II. LOCAL DEMAND GENERATION

According to the data provided by the electrical distributor in the region; the highest demand in 2012 was 25 MW, while the minimum was 4,4 MW [1]. The average demand, along the year and days of the week, is:

TABLE I. AVERAGE POWER DEMAND (MW)

On weekdays Weekend

Summer 12,52 9,97

Autumn 8,36 7,46

Winter 12,20 10,75

Spring 10,06 8,16

During winter and summer, the demand is higher than in other seasons. Regardless of the season, the demand on weekdays is higher than the one during the weekend.

III. EXISTING POWER GENERATION UNITSEVALUATION

There are several power installations around Andújar in a perimeter of 20 km:

- Two regulating reservoirs, Encinarejo and Jándula, that have a high manageability and installed capacity; and the run-of-river power plant of Valtodano. Nevertheless, both hydroelectric power stations are regulated by the Guadalquivir Hydrographic Confederation and they just operate on irrigation periods and the run-of-river power plant relies on the weather of each season

- There is also a thermal installation of biomass Aldebaran, which employs local waste of olive oil production and has a high manageability too.

- Finally, there are two photovoltaic power plants; that rely on the weather of each season as it also happens with the run-of-river power plant of Valtodano.

TABLE II. POWER AND MANAGEABILITY OF EACH UNIT [1]

Name Technology Manageability Installed Power (MW)

Encinarejo Regulating reservoir Higha

8,32

Jándula Regulating reservoir 15

Valtodano Run-of-river power plant Low 3,15

Aldebarán Thermical. Olive biomass High 6

Solar group Photovoltaic None 3,5a. Regulated by Guadalquivir Hydrographical Confederation

IV. ADVANTAGE OF MSW WITH THE MOSTSUITABLE TECHNOLOGY

The Municipal Solid Waste (MSW) generated at homes, stores, offices and services; is the main resource of biomass existing in every neighborhood of any village.

According to Eurostat database, a Spaniard generates between 530 and 550 kg of MSW, depending on the year. For this study, it will be consider 535 kg due to the decreasing trend in recent years. The organic fraction accounts for 50% of all MSW. In Andújar, where live around 39.000 inhabitants, 10.237,20 tons of organic wastes are generated each year. [2].

The plasma gasification technology has been considered to treat the MSW. The generated synthesis gas will be used in a Rankine cycle and in hydrogen fuel cells, in order to obtain electrical power.

First, it will be used a converter plasma system to treat the MSW, obtaining a synthesis gas (mainly CO and H2). The synthesis gas has impurities and a temperature of 1.200 °C, when it leaves the converter system. This high temperature will be circulated for two purposes: to produce electricity on a Rankine cycle and to dry the entrance wastes at the system. Later, the gas will be passed to different cleaning stages (fabric filters, Quench and Scrubber system). Figure I and Figure II summarize the converter system process and show the sketch of the vessel.

FIGURE I. PLASMA CONVERTER SYSTEM PROCESS [3]

FIGURE III. VESSEL OF PLASMA CONVERTER SYSTEM [3]

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International Conference on Renewable Energy Research and Applications Madrid, Spain, 20-23 October 2013

ICRERA 2013 618

TABLE III. WEIGHT PERCENTAGE OF THE CLEAN SYNGAS BEFOREWATER GAS SHIFT REACTION PROCESS [3]

Once the gas is cleaned and cooled, it can be stored and then produce power in a gas-cycle or with fuel cells. On this project, it will be chosen the fuel cells choice because they have higher energy efficiency and the only sub product is water. The main disadvantage of this technology is the need for using high-purity hydrogen, to avoid decreasing the performance of the fuel cell. For this last reason, it is necessary an extra stage to remove the presence of CO, with a Water-Gas Shift Reactor. Nowadays, one of the most developed fuel cell in the market is the proton exchange membrane (PEM), so this is the fuel cell that will be used in the micro-grid.

FIGURE IIIII. PROCESS PREVIOUS TO THE USE OF FUELCELLS

The volume of flow of the gas is 995,57 kg/h and it has a higher heat value (HHV) of 19,73 MJ/kg. [3]

The power generated by the Rankine cycle is 91,92 kW with a total cycle performance of 36,55 %. With the remaining heat is possible to reduce the humidity of the entrance waste in a 30%. The final flow of hydrogen obtained, amount to 63 kg/h with purity above 98%.

V. MICRO-GRID DESIGN

This section analyzes the combination in the grid of the different generation units in the most favorable way. The hydrogen production is settled to the daily generation, it is estimated a fuel cell capacity up to 11 MW in order to cover greater electricity demand in periods of high power consumption and to storage the hydrogen as gas for periods of lower consumption.

FIGURE IV. FORECASTING AND MEETING DEMAND

The previous figure shows the trend of the maximum demand (red line) and an estimation of how the different power installations meet the demand on each month of the year. The fuel cells and the biomass power plants cover the base power in this system. Then the regulating reservoirscover the intermediate demand the periods they operate. And the run-of-river power plant and the photovoltaic groups will be used as occasional support or to deliver power to the main grid.

FIGURE V. MICRO-GRID GENERAL SKETCH

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International Conference on Renewable Energy Research and Applications Madrid, Spain, 20-23 October 2013

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VI. OVERALL MICRO-GRID ECONOMICAL EVALUATION

This section carries out the economical evaluation of thewhole micro-grid. On the table below, it is shown the average production price of each technology according to each initial plant investment and maintenance and operational costs, updated each year according to the Consumer Price Index (CPI). The overall average production price is 0,0948 €/kWh and it is necessary to add to this price the corresponding electricity supply costs like distribution costs, commercial management costs and taxes (which are estimated to add up to 0,0435 €/kWh). Therefore, the total electricity price comes to 0,1383 €/kWh which is a competitive price compared to the average Last Resort Rate (LRR), which amounts to 0,1389 €/kWh, in 2013.[4]

TABLE IV. AVERAGE PRODUCTION PRICE (€/KWH)

Mini-hydraulic Photovoltaic Aldebaran

biomassRankine

cyclePlasma

gasification0,0521 0,1465 0,0832 0,1423 0,0502

FIGURE VI. AVERAGE PRODUCTION PRICE (€/KWH)

The total investment of all the installations amount to 88,44 M€; where the investment time horizon is 25 years with an estimated CPI of 2,5% and a discount rate of 10%. Table IV shows some important ratios like; Net Present Value (NPV), Internal Rate of Return (IRR) and Payback Period (PP).

As the NPV is positive and the IRR is higher than the discount rate, it is said that the project is profitable.

TABLE V. PERFORMANCE RATIOS

NPV [M€] IRR [%] PP [years]

5,94 10,78 10

REFERENCES

[1] Power local company, database (2012) [2] Eurostat- European statistics database.

http://epp.eurostat.ec.europa.eu/portal/page/portal/environment/data/database

[3] Materiales Renovados, engineering company. [4] http://tarifasgasluz.com/faq/tarifa-de-ultimo-recurso

620

International Conference on Renewable Energy Research and Applications Madrid, Spain, 20-23 October 2013

ICRERA 2013 620