Hydrogen and syngas yield from residual branches of oil palm tree using steam gasification

Wastes produced during oil palm production from agro-industries have great potential as a source of renewable energy in agriculturally rich countries, such as Thailand and Malaysia. Clean chemical energy recovery from oil palm residual branches via steam gasification is investigated here. A semi-batch reactor was used to investigate the gasification of palm trunk wastes at different reactor temperatures in the range of 600 to 1000 °C. The steam flow rate was fixed at 3.10 g/min. Characteristics and overall yield of syngas properties are presented and discussed. Results show that gasification temperature slightly affects the overall syngas yield. However, the chemical composition of the syngas varied tremendously with the reactor temperature. Consequently, the syngas heating value and ratio of energy yield to energy consumed were found to be strongly dependent on the reactor temperature. Both the heating value and energy yield ratio increased with increase in reactor temperature. Gasification duration and the steam to solid fuel ratio indicate that reaction rate becomes progressively slower at reactor temperatures of less than 700 °C. The results reveal that steam gasification of oil palm residues should not be carried out at reactor temperatures lower than 700 °C, since a large amount of steam is consumed per unit mass of the sample in order to gasify the residual char.     

Cogeneration potential in the Columbian palm oil industry: Three case studies

The palm oil mills are characterized by the availability of considerable amounts of by-products of high-energy value such as empty fruit bunches (EFB), fibers, shells and liquid effluents with high content of organics called palm oil mill effluent (POME). A palm oil mill produces residues equivalent to almost three times the amount of oil produced by biomass, showing a huge potential for increasing the power efficiency of the plants and installed power, mainly by the use of by-products in cogeneration plants with high steam parameters and by reducing steam consumption in process. The objective of this paper is to present the results of the study about the cogeneration potential for three representative palm oil mills located in two important palm oil producing regions in Colombia (South-America), fifth palm oil producers of the world. The sizing of the cogeneration system was made assuming it operation during the greatest possible number of hours throughout the year (based on the seasonal availability of fruit) considering parameters for the steam at 2 MPa and 350 °C, using a condensing-extraction turbine. The balance of mass and energy was made by using the Gate Cycle Enter Software, version 5.51, to estimate the potential of electricity generation. The results showed that for fresh fruit bunch (FFB) processing capacities between 18 and 60 t FFB h⁻¹, it is possible to have surplus power ranging between 1 and 7 MW, if the plants are self-sufficient in electric energy and steam for process. With an average Capacity Factor (approximately 0.4), it is possible to expect a generation index of 75 and 160 kWh t⁻¹ FFB when the processing plant is operating or shutdown, respectively, 3 or 4 times better than when a traditional system with a back-pressure steam turbines is used. This analysis used up to 60% of EFB produced in plant as fuel, considering its value as fertilizer for the palm crop. Several economic conditions were considered to estimate the economic and technical feasibility of cogeneration systems in palm oil mill for Colombian palm oil sector.     

Supercritical steam cycles and biomass integrated gasification combined cycles for sugarcane mills

Back in 1970s and 1980s, cogeneration plants in sugarcane mills were primarily designed to consume all bagasse, and produce steam and electricity to the process. The plants used medium pressure steam boilers (21 bar and 300 °C) and backpressure steam turbines. Some plants needed also an additional fuel, as the boilers were very inefficient. In those times, sugarcane bagasse did not have an economic value, and it was considered a problem by most mills. During the 1990s and the beginning of the 2000s, sugarcane industry faced an open market perspective, thus, there was a great necessity to reduce costs in the production processes. In addition, the economic value of by-products (bagasse, molasses, etc.) increased, and there was a possibility of selling electricity to the grid. This new scenario led to a search for more advanced cogeneration systems, based mainly on higher steam parameters (40–80 bar and 400–500 °C). In the future, some authors suggest that biomass integrated gasification combined cycles are the best alternative to cogeneration plants in sugarcane mills. These systems might attain 35–40% efficiency for the power conversion. However, supercritical steam cycles might also attain these efficiency values, what makes them an alternative to gasification-based systems. This paper presents a comparative thermoeconomic study of these systems for sugarcane mills. The configurations studied are based on real systems that could be adapted to biomass use. Different steam consumptions in the process are considered, in order to better integrate these configurations in the mill.     

Analysis of biomass-residue-based cogeneration system in palm oil mills

Palm oil mills in Malaysia operate on cogeneration system using biomass residue as fuel in the boiler. The boiler produces high pressure and temperature steam which expands in a backpressure steam turbine and produces enough electric power for the internal needs of the mill. The exhaust steam from the turbine goes to an accumulator which distributes the steam to various processes in the mill.The study were made on seven palm oil mills in the Perak state in Malaysia. The primary objectives of the study are to determine boiler and turbine efficiencies, energy utilization factor, oil extraction rate and heat/power ratio for various palm oil mills working under similar conditions and adopting same processes. The palm oil industry is one of those rare industries where very little attempt is made to save energy. The energy balance in a typical palm oil mill is far from optimum and there is considerable scope for improvement. Bench-marking is necessary for the components in the mill. Energy-use bench-marking can give an overview of energy performance of the mills. The calculations were done to get net gain in power when back pressure turbine is replaced by a condensing turbine.It was found that the boiler and turbine have low thermal efficiencies compared to conventional ones used in power plants due to non-homogeneity and non-uniform quality of the fuel. The extraction rate was around 0.188. The use of condensing turbine increase the power output by 60% and the utilization factor was found to be 65% for the cogeneration system.     

Role of sodium hydroxide in the production of hydrogen gas from the hydrothermal gasification of biomass

The role of sodium hydroxide as a promoter of hydrogen gas production during the hydrothermal gasification of glucose and other biomass samples has been investigated. Experiments were carried out in a batch reactor with glucose and also in the presence of the alkali from 200 °C, 2 MPa to 450 °C, 34 MPa at constant water loading. Without sodium hydroxide, glucose decomposed to produce mainly carbon dioxide, water, char and tar. Furfural, its derivatives and reaction products dominated the ethyl acetate extract of the water (organic fraction) at lower reaction conditions. This indicated that the dehydration of glucose to yield these products was unfavourable to hydrogen gas production. In the presence of sodium hydroxide however, glucose initially decomposed to form mostly alkylated and hydroxylated carbonyl compounds, whose further decomposition yielded hydrogen gas. It was observed that at 350 °C, 21.5 MPa, half of the optimum hydrogen gas yield had formed and at 450 °C, 34 MPa, more than 80 volume percent of the gaseous effluent was hydrogen gas, while the balance was hydrocarbon gases, mostly methane (≥10 volume percent). Other biomass samples were also comparably reacted at the optimum conditions observed for glucose. The rate of hydrogen production for the biomass samples was in the following order; glucose > cellulose, starch, rice straw > potato > rice husk.     

Thermodynamic optimization of biomass gasification for decentralized power generation and Fischer–Tropsch synthesis

In recent years, biomass gasification has emerged as a viable option for decentralized power generation, especially in developing countries. Another potential use of producer gas from biomass gasification is in terms of feedstock for Fischer–Tropsch (FT) synthesis – a process for manufacture of synthetic gasoline and diesel. This paper reports optimization of biomass gasification process for these two applications. Using the non–stoichometric equilibrium model (SOLGASMIX), we have assessed the outcome of gasification process for different combinations of operating conditions. Four key parameters have been used for optimization, viz. biomass type (saw dust, rice husk, bamboo dust), air or equivalence ratio (AR = 0, 0.2, 0.4, 0.6, 0.8 and 1), temperature of gasification (T = 400, 500, 600, 700, 800, 900 and 1000 °C), and gasification medium (air, air–steam 10% mole/mole mixture, air–steam 30%mole/mole mixture). Performance of the gasification process has been assessed with four measures, viz. molar content of H₂ and CO in the producer gas, H₂/CO molar ratio, LHV of producer gas and overall efficiency of gasifier. The optimum sets of operating conditions for gasifier for FT synthesis are: AR = 0.2–0.4, Temp = 800–1000 °C, and gasification medium as air. The optimum sets of operating conditions for decentralized power generation are: AR = 0.3–0.4, Temp = 700–800 °C with gasification medium being air. The thermodynamic model and methodology presented in this work also presents a general framework, which could be extended for optimization of biomass gasification for any other application.     

Proposal and analysis of a novel ammonia–water cycle for power and refrigeration cogeneration

Cogeneration has improved sustainability as it can improve the energy utilization efficiency significantly. In this paper, a novel ammonia-water cycle is proposed for the cogeneration of power and refrigeration. In order to meet the different concentration requirements in the cycle heat addition process and the condensation process, a splitting /absorption unit is introduced and integrated with an ammonia–water Rankine cycle and an ammonia refrigeration cycle. This system can be driven by industrial waste heat or a gas turbine flue gas. The cycle performance was evaluated by the exergy efficiency, which is 58% for the base case system (with the turbine inlet parameters of 450 °C/11.1 MPa and the refrigeration temperature below −15 °C). It is found that there are certain split fractions which maximize the exergy efficiency for given basic working fluid concentration. Compared with the conventional separate generation system of power and refrigeration, the cogeneration system has an 18.2% reduction in energy consumption.     

An investigation into steam gasification of biomass for hydrogen enriched gas production in presence of CaO

Biomass steam gasification could be an attractive option for sustainable hydrogen production. Biomass, regarded as carbon neutral emitter, could be claimed as carbon negative emitter if carbon dioxide produced is captured and not allowed to emit to the environment during the process. Thus here an experimental study is carried out to find out the potential of hydrogen production from steam gasification of biomass in presence of sorbent CaO and effect of different operating parameters (steam to biomass ratio, temperature, and CaO/biomass ratio). Product gas with hydrogen concentration up to 54.43% is obtained at steam/biomass = 0.83, CaO/biomass = 2 and T = 670 °C. A drop of 93.33% in carbon dioxide concentration was found at CaO/biomass = 2 as compared to the gasification without CaO. Mathematical model based on Gibbs free energy minimization has been developed and is compared with the experimental results.     

Microalgae Chlorella as a potential bio-energy feedstock

Microalgae are promising biomass species owing to their fast growth rate and high CO₂ fixation ability as compared to terrestrial plants. Microalgae have long been recognized as potentially good source for biofuel production because of their high oil content and rapid biomass production. In this study Chlorella sp. MP-1 biomass was examined for its physical and chemical characteristics using Bomb calorimeter, TGDTA, CHN and FTIR. The proximate composition was calculated using standard ASTM methodology. Chlorella sp. MP-1 biomass shows low ash (5.93%), whereas high energy (18.59 MJ/kg), carbohydrate (19.46%), and lipid (28.82%) content. The algal de-oiled cake was characterized by FTIR spectroscopy and thermogravimetric study at 10 °C/min and 30 °C/min to investigate its feasibility for thermo-chemical conversion. The present investigation suggests that within the realm of biomass energy technologies the algal biomass can be used as feedstock for bio and thermo-chemical whereas the de-oiled cake for thermo-chemical conversion thereby serving the demand of second generation biofuels.     

Implementation of a heat recovery unit in a proton exchange membrane fuel cell system

A heat recovery unit (HRU) has been developed and implemented in a proton exchange membrane (PEM) fuel cell cogeneration system that generates electricity and hot water efficiently. It consists of a stack coolant circuit, a heat exchanger, and a heat recovery circuit. An intelligent thermal control algorism is proposed as well to manage the cogeneration system. The HRU together with the control scheme has managed the fuel cell cogeneration system properly and efficiently. The stack coolant inlet temperature (SCIT) is well controlled at the preset temperatures (55 °C and 59 °C) under different external loads (0–3 kW). Results also show that the dynamics of the SCIT is closely related to the actions of the secondary fluid pump. Up to 50% fuel energy can be recovered thermally in the present cogeneration system. Examination of the external-load effects reveals that increasing external loads increases the electrical efficiency but decreases the heat recovery efficiency slightly. The maximum efficiency as a combination of heat and power is 82% based on hydrogen's lower heating value.     

On better utilization of gas turbines in Kuwait

The Kuwaiti Ministry of Electricity and Water installed 16 gas turbine (GT) units of 2000 MW total generating capacity at Azzour South power plant (PP) and Sabbyia PP. These units are operating as a simple GT cycle by gas or oil fuel. The GT unit power output in Azzour PP is 163 MW at 15 °C ambient temperature (ISO conditions), and 125 MW at 46 °C (design outside air conditions). This paper suggests four variants for better utilization of these GT units. The first variant is to utilize these GT during off-peak hours to operate seawater reverse-osmosis desalting system. This increases the badly needed installed desalting capacity, decreases the specific energy consumed for desalting, and solves the problem of low water-to-power production ratio. The second variant is to add heat recovery steam generator to produce steam. This steam is used to operate multi-stage flashing units for more desalted water with no additional fuel energy. In the third variant, a gas/steam combined cycle is proposed to increase significantly both the installed capacity and efficiency. The fourth variant deals with cooling intake air to the compressor to increase the unit capacity when needed in hot days.     

Development of a case-based reasoning prototype for cogeneration plant design

This paper deals with the design problem associated with natural gas cogeneration systems. Despite the task complexity, this design process is strongly based on knowledge that experts formally apply in their activities. Through an appropriate knowledge representation scheme this study demonstrates that the knowledge-based system (KBS) is an approach well-suited to cogeneration plant design. The research involves the use of rule-based expert systems (RBES) and case-based reasoning (CBR). In this paper, the basic concepts of the CBR technique and a CBR prototype for assistance in cogeneration plant design are presented. An RBES prototype for natural gas cogeneration system design previously developed by the authors is used to generate cases for the CBR prototype. A solution generated by the CBR prototype for a plant design requiring 4 MW of power and 0.7 kg/s of saturated steam at 0.9 MPa is presented. The application of CBR in cogeneration plant design represents an original and important contribution of this work.     

Structural analysis of bio-oils from sub-and supercritical water liquefaction of woody biomass

Woody biomass was liquefied by water in an autoclave in the reaction temperature range of 280–420 °C with sodium carbonate as the catalyst. The experimental results show that the yield of the main liquefaction product (heavy oil) was significantly influenced by the process conditions. The maximum yield of heavy oil was obtained at reaction temperature 380 °C. The heavy oils obtained at different reaction temperature were analyzed by Fourier transform infrared spectroscopy (FTIR) and gas chromatography/mass spectrometry (GC/MS). The analytical results show the heavy oil is complex compound that contain hydrocarbon, aldehyde, ketone, hydroxybenzene and ester.     

A comparative study of vegetable oil methyl esters (biodiesels)

In the present study, rubber seed oil, coconut oil and palm kernel oil, which are locally available especially in Kerala (India), are chosen and their transesterification processes have been investigated. The various process variables like temperature, catalyst concentration, amount of methanol and reaction time were optimized. Biodiesel from rubber seed oil (with high free fatty acid) was produced by employing two-step pretreatment process (acid esterification) to reduce acid value from 48 to 1.72 mg KOH/g with 0.40 and 0.35 v/v methanol-oil ratio and 1.0% v/v H₂SO₄ as catalyst at a temperature of 63(±2) °C with 1 h reaction time followed by transesterification using methanol-oil ratio of 0.30 v/v, 0.5 w/v KOH as alkaline catalyst at 55(±2) °C with 40 min reaction time to yield 98-99% biodiesel. Coconut oil and palm oil, being edible oils, transesterification with 0.25 v/v methanol-oil ratio, 0.50% w/v KOH as at 58(±2) °C, 20 min reaction time for coconut oil and 0.25% v/v methanol-oil ratio, 0.50% w/v KOH as alkaline catalyst at 60(±2) °C for palm kernel oil will convert them to 98-99% biodiesel. The brake thermal efficiency of palm oil biodiesel was higher with lower brake specific fuel consumption, but rubber seed oil biodiesel(ROB) showed less emission (CO and NO_x) compared to other biodiesels.     

Exergoeconomic assessment of a geothermal assisted high temperature steam electrolysis system

Exergoeconomic formulations and procedure including exergy flows and cost formation and allocation within a high temperature steam electrolysis (HTSE) system are developed, and applied at three environmental temperatures. The cost accounting procedure is based on the specific exergy costing (SPECO) methodology. Exergy based cost-balance equations are obtained by fuel and product approach. Cost allocations in the system are obtained and effect of the second-law efficiency on exergetic cost parameters is investigated. The capital investment cost, the operating and maintenance costs and the total cost of the system are determined to be 422.2, 2.04, and 424.3 €/kWh, respectively. The specific unit exergetic costs of the power input to the system are 0.0895, 0.0702, and 0.0645 €/kWh at the environmental temperatures of 25 °C, 11 °C, and −1 °C, respectively. The exergetic costs of steam are 0.000509, 0.000544, and 0.000574 €/kWh at the same environmental temperatures, respectively. The amount of energy consumption for the production of one kg hydrogen is obtained as 133 kWh (112.5 kWh power + 20.5 kWh steam), and this corresponds to a hydrogen cost of 1.6 €/kg H₂.     

Oxygen-reduction activity of silk-derived carbons

Carbonized silk fibroin (CS), which is free of metallic elements, showed high catalytic activity for oxygen-reduction reaction (ORR). The catalytic activity of CS for ORR was greatly enhanced by steam activation forming silk-derived activated carbon (CS-AC). The surface morphology, surface area, pore structure and remaining nitrogen species of the CSs were compared with those of the CS-ACs. The open-circuit potential and the power density of a polymer electrolyte fuel cell using a CS900-AC, which was heat-treated at 900 °C prior to the steam activation, and a platinum/C (C: carbon black) anode under pure oxygen and hydrogen gases, respectively, both at 0.2 MPa, were 0.92 V and 142 mW cm⁻² at 80 °C. The ORR on the activated carbon, CS900-AC, proceeded with a 3.5-electron reaction at 0.6 V (vs. RHE); however, this was improved to a 3.9-electron reaction with the addition of zirconium oxide at 20 wt% to CS900-AC.     

Effect of biomass leaching on H2 production,ash and tar behavior during high temperature steam gasification (HTSG) process

The effect of biomass water leaching on H₂ production, as well as, prediction of ash thermal behavior and formation of biomass tar during high temperature steam gasification (HTSG) of olive kernel is the main aim of the present work. Within this study raw olive kernel samples (OK₁, OK₂) and a pre-treated one by water leaching (LOK₂) were examined with regard to their ash fouling propensity and tar concentration in the gaseous phase. Two temperatures (T = 850 and 950 °C) and a constant steam to biomass ratio (S/B = 1.28) were chosen in order to perform the steam gasification experiments. Results indicated that considering the samples' ash thermal behavior, it seemed that water leaching improved the fusibility behavior of olive kernel; however, it proved that water leaching does not favour tar steam reforming, while at the same time decreases the H₂ yield in gas product under air gasification conditions, due to possible loss of the catalytic effect of ash with water leaching.     

Hydrogen production from ethanol over Co/ZnO catalyst in a multi-layered reformer

A Co/ZnO catalyst was prepared by coprecipitation method, and was applied for ethanol steam reforming. The effect of reaction conditions on the ethanol steam reforming performance was studied in the temperature ranges from 400 °C to 600 °C and the space velocity ranges from 10,000 h⁻¹ to 120,000 h⁻¹ in a fixed bed reactor. The Co/ZnO showed high activity with an ethanol conversion of 97% and a H₂ concentration of 73% at a gas hourly space velocity of 40,000 h⁻¹ and a moderately low temperature of 450 °C. EXAFS analysis for fresh and spent samples confirms that Co phase maintains during reaction. The catalyst was then loaded into a multi-layered reformer of which the design concept allows for integrating endothermic steam reforming, exothermic combustion and evaporation in a reactor. The performance of the compact reformer demonstrated that the hydrogen production rate satisfy a PEMFC stack power level of 540 W suitable for portable power supplies.     

Proposal and analysis of a dual-purpose system integrating a chemically recuperated gas turbine cycle with thermal seawater desalination

A novel cogeneration system is proposed for power generation and seawater desalination. It combines the CRGT (chemically recuperated gas turbine) with the MED-TVC (multi-effect thermal vapor compression desalination) system. The CRGT contains a MSR (methane-steam reformer). The produced syngas includes plenty of steam and hydrogen, so the working medium flow increases and NO_x emissions can achieve 1 ppm low. However, the water consumption is large, ∼23 t/d water per MW power output. To solve this problem and produce water for sale, MED-TVC is introduced, driven by exhaust heat. Such a dual-purpose plant was analyzed to investigate its performance and parameter selection, and compared with four conventional cogeneration systems with the same methane input. Some main results are following: In the base case of the CRGT with a TIT of 1308 °C and a compression ratio of 15, the MED-TVC with 9 effects, the specific work output, performance ratio and CRGT-consumed water ratio are 491.5 kJ/kg, 11.3 and 18.2%, respectively. Compared with the backpressure ST (steam turbine)/CC (combined cycle) plus MED/MSF (multistage flash), the CRGT + MED has better thermal performance, lower product cost and shorter payback period, which indicates the CRGT + MED dual-purpose system is a feasible and attractive choice for power and water cogeneration.     

Integrated catalytic adsorption (ICA) steam gasification system for enhanced hydrogen production using palm kernel shell

This paper investigates the integrated catalytic adsorption (ICA) steam gasification of palm kernel shell for hydrogen rich gas production using pilot scale fluidized bed gasifier under atmospheric condition. The effect of temperature (600–750 °C) and steam to biomass ratio (1.5–2.5 wt/wt) on hydrogen (H₂) yield, product gas composition, gas yield, char yield, gasification and carbon conversion efficiency, and lower heating values are studied. The results show that H₂ hydrogen composition of 82.11 vol% is achieved at temperature of 675 °C, and negligible carbon dioxide (CO₂) composition is observed at 600 °C and 675 °C at a constant steam to biomass ratio of 2.0 wt/wt. In addition, maximum H₂ yield of 150 g/kg biomass is observed at 750 °C and at steam to biomass ratio of 2.0 wt/wt. A good heating value of product gas which is 14.37 MJ/Nm³ is obtained at 600 °C and steam to biomass ratio of 2.0 wt/wt. Temperature and steam to biomass ratio both enhanced H₂ yield but temperature is the most influential factor. Utilization of adsorbent and catalyst produced higher H₂ composition, yield and gas heating values as demonstrated by biomass catalytic steam gasification and steam gasification with in situ CO₂ adsorbent.