Electrical performance evaluation of Johansson biomass gasifier system coupled to a 150 KVA generator

doi:10.1016/j.renene.2014.06.018

Renewable Energy

Volume 71, November 2014, Pages 695-700

https://doi.org/10.1016/j.renene.2014.06.018 Get rights and content

Highlights – giving the essence of the research and the distinctive thing about it

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The study investigated the performance of a biomass gasifier system when operated on a full load.
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The cold gas efficiency and overall efficiency of the system was found to be 88.11% and 20.5% respectively.
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The specific consumption rate of the biomass gasifier system was found to be 1.075 kg/kWh.

Abstract

The economic development of any community or society at large is directly linked to energy availability and usage. Concern for climate change due to intense use of fossil fuel for energy production has increased interest in alternative energy technologies such as biomass gasification. A Johansson biomass gasifier system at Melani village in Eastern Cape South Africa was installed to assess the viability of biomass gasification for energy production in South Africa. This system utilizes chunks of wood coming from a sawmill industry located nearby, which produces large quantities of biomass waste that pose a challenge in terms of disposal. A study on the implementation of the latter gasification project has been carried out. Therefore this present study aims at evaluating the performance of the system when operated on a full electrical load. A custom-built gas and temperature profiling system was used to measure the gas profiles from which the gas heating value was calculated. A measuring balance/scale was used to measure the quantity of wood fed into the gasifier. A dummy load bank was constructed using 12 kW water heating elements connected such that they draw maximum power from each of the three phases. A power meter was used to measure the current, voltage, power as well as energy from the generator during operation. A cold gas efficiency of 88.11% was obtained and the overall efficiency from feedstock to electrical power was found to be 20.5% at a specific consumption rate of 1.075 kg/kWh.

Introduction

Biomass is an organic material that stores solar energy via photosynthesis and in turn creates a source of energy in form of carbon, hydrogen and oxygen compound. It contains less carbon but more oxygen and a lower heating value than the conventional fossil fuel [1]. Conversion of biomass into other forms of energy such as electrical energy and heat energy is a promising alternative to fossil fuel due to its renewable nature and availability. Two major conversion processes (conversion to power, heat, transportation fuel, chemicals and methane gas) exist but the choice of any is dependent on the end use application, environmental impact, economic factor, the type and properties of the biomass [2], [3]. These processes are thermochemical conversion and Biochemical conversion.

Biochemical conversion involves the fermentation of plant material with the use of yeast or genetically modified microorganisms to produce ethanol and anaerobic digestion of plant material to produce methane gas. Thermochemical conversion involves the thermal conversion of biomass material at different temperatures and oxygen environment. It includes pyrolysis, gasification and combustion. This research is focused on biomass gasification, which is the thermal conversion of carboneous material in a controlled oxygen, air or steam environment to yield a mixture of gases known as producer gas and usually referred to as syngas. This thermochemical process takes place in a gasifier/reactor which comes in different designs namely; downdraft, updraft and cross draft (fixed bed), bubbling, circulating and twin bed (fluidized bed), coaxial and opposed jet (entrained flow) [4]. The advantages and disadvantages of these types of gasifiers are well known and documented [5], [6].

The downdraft gasifier has an advantage of producing gas with low tar concentration, which makes it suitable for operating gas engines and turbines used for electricity generation. The concentration of tar in the producer gas generated from a downdraft gasifier is relatively low when compared to that from updraft gasifier. It ranges between 10 and 100 g/Nm³ for downdraft gasifier and 50 and 500 g/Nm³ for updraft gasifier [7]. Downdraft gasifiers are mostly used due to the earlier mentioned advantage. Dogru et al. [8] investigated the gasification characteristics of hazelnut shell using a pilot scale downdraft gasifier with 5 kW electrical outputs. An experimental study has been carried out by Sharma [4] on a 75 kW th downdraft gasifier system. The temperature profile was obtained along side with gas composition, calorific value and pressure drop across the porous gasifier bed. Jayah et al. [9] calibrated a computer program from an experimental result in order to investigate the impact of some operating and design parameters on conversion efficiency of a downdraft gasifier. The operating parameters were moisture content, particle size and inlet air temperature and the design parameters were throat angle and heat loss.

The aim of this study is to analyze the performance of a 150 kVA Johansson biomass gasifier system when operated on a full load bank. The load bank comprises of 12 kW heating elements connected in parallel so as to draw maximum power from the generator on each of the three phases.

Section snippets

Description of a Johansson biomass gasifier system

Fig. 1 represnts the different components of Johansson biomass gasifier system. This system comprises of a reactor/gasifier, cyclone, scrubber, sawdust filter, safety filter, condensate tank and electrical generator.

The reactor consists of four zones corresponding to the four gasification processes, namely: drying, pyrolysis, oxidation and reduction. The feedstock (pine wood) is fed into the gasifier hopper through the lid using an electrically controlled winch. Air containing oxygen and some

Gas analysis, ultimate and proximate analysis

The mass of the feedstock was determined using a measuring balance/scale before feeding into the gasifier hopper. The ultimate and proximate analyses were done to determine the physical and chemical properties of the pine wood used for this study. The calorific value of the material was determined using a CAL2K oxygen Bomb calorimeter.

Gas analysis was undertaken using a custom-built Gas and Temperature Profiling System (GTPS), which employs non-dispersive infrared gas sensors for measurement of

Wood analysis

Table 2 presents the proximate and ultimate analyses of a random sample of wood generated from the sawmill industry. The proximate and ultimate analysis were determined to establish the suitability of the feedstock for gasification purposes. The obtained moisture content is within the range required for downdraft gasifier. Usually high moisture content is unfavorable during gasification since it lowers combustion zone temperature and thus leads to production of low quality gas. High volatile

Conclusion

The performance of a Johansson biomass gasifier evaluated in this study showed that the system was producing power above its power rating when operated at full load. The calorific value of the gas was estimated to be 6.3 MJ/Nm³ at an equivalence ratio of 0.29. This agreed well with literature as summarized in Table 4. A cold gas efficiency of 88.11% obtained indicates stability in the gasifier operating condition. This was evident also in the calorific value of the gas obtained. The study also

Acknowledgment

The authors would like to acknowledge South African Clean Energy Solutions limited R8000 for funding the construction of the load bank and the experimental part of the research. We would also like to acknowledge the National Research Foundation R40000, Eskom R4.5million and Govan Mbeki Research and development centre R8000 at the University of Fort Hare for Funding.

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Electrical performance evaluation of Johansson biomass gasifier system coupled to a 150 KVA generator

Highlights – giving the essence of the research and the distinctive thing about it

Abstract

Introduction

Section snippets

Description of a Johansson biomass gasifier system

Gas analysis, ultimate and proximate analysis

Wood analysis

Conclusion

Acknowledgment

Bioresour Technol

Procedia Engineering

Renew Sustain Energy Rev

Biomass Bioenergy

Energy

Fuel Process Technol

Energy

Biomass Bioenergy

Biomass Bioenergy

A review of fixed bed gasification systems for biomass, agricultural engineering international: the CIGR

Ejournal, Invited Overview