Calorific Value Of Syngas

[Rafael Nowning]

Syngasalso called a synthesis gas, is a mix of molecules containing hydrogen, methane, carbon monoxide, carbon dioxide, water vapours, as well as other hydrocarbons and condensable compounds.It is a majority product of high temperature pyrolysis carried on any biomass, residues and waste.When produced in pyrolysis, it is created by the vaporisation of volatile compounds from the raw material thanks to the heat, which induces a set of complex reactions.

The chemical composition of syngas and proportion of its molecules is highly dependent on the raw material characteristics and conditions of the treatment process. Biogreen technology allows a consistent generation of syngas fuels thanks to the stable, repeatable treatment conditions and possibility of adapting the processing temperature according to the demand.

Generated synthetic gas leaving the Biogreen reactor is a hot mixture of condensable and non-condensable phases. The composition of such blend depends on source material (feedstock) and pyrolysis operating conditions. Gases from pyrolysis typically contain significant quantities of methane, hydrogen, carbon monoxide, and dioxide, as well as higher hydrocarbons that build their calorific value and make them important fuel for the chemical and energy industries.

In the hot state, synthetic gas contains condensable and permanent gases and can be considered as an alternative, or renewable energy source, and as a fuel for high temperature syngas burners.New Paragraph

Received syngas composition is strongly dependent on several factors, including the properties of treated material, temperature of process, applied residence time and physical structure of raw feedstock, for details, see chapter What influences pyrolysis process results? Below we provided an example compositions of non-condensable fractions of gases measured at ambient temperature.

The main application of produced syngas is typically the generation of power and heat. This can be realised either in stand-alone combined heat and power (CHP) plants or through co-firing of the product gas in large-scale power plants.

Syngas from pyrolysis is a combustible gas and can be used for the production of power in many types of equipment, from steam cycles through gas engines and turbines. While the usages in boilers for steam cycles typically do not require extensive gas treatment before the power generation, the gas engines request a higher degree of purification and preparation.

The stability and consistency of fuel provided to the internal combustion engine is one of the key factors of process. It is ensured by feedstock stability and the precisely controlled treatment conditions in Biogreen pyrolysis unit.ent temperature

The high-temperature processes of pyrolysis allow to create significant quantities of syngas with notable concentrations of carbon monoxide, hydrogen and methane. The interest in production of synthetic natural gas through the methanation of H2 and CO is increasing fast.

Following this interest, ETIA partners with European leader in gas transportation systems, GRTgaz. The objective of alliance is construction of a pilot plant dedicated to produce the synthetic methane from waste and biogenic resources.

Biogreen is pyrolysis equipment suitable for production of calorific syngas for all the applications described below. The patented, electrically heated reactor allows to achieve continuous, repeatable conditions of treatment and stable production of syngas. Thanks to the precise control of the carried process and multiple industrial references, Biogreen remains a first choice of customers looking for consistent and reliable production.

Syngas for use in integrated gasification combined cycle (IGCC) applications must be free of contaminants such as particulates and trace metals which could cause damage to the gas turbine. The ratio of hydrogen to carbon monoxide (CO) is not as important as in other applications which use syngas derived from gasification, at least if the turbine has been designed to handle increased hydrogen content. Some gasification technologies, such as catalytic gasification, may result in the syngas having relatively high hydrocarbon content, making it more similar to natural gas, which is ideal for utilization in combustion turbines. This may be explained by the simple fact that gas turbines developed for use in IGCC applications with syngas have invariably been based on natural gas combustion turbines. Despite the similarities between syngas and natural gas, there are differences which impact the design of the combustion turbines they fuel.

Gasification-derived syngas differs from natural gas in terms of calorific value, composition, flammability characteristics, and contaminants. Oxygen-blown, entrained flow IGCC plants typically produce syngas with a heating value range of 250 to 400 Btu/ft3 (HHV basis), which is much lower than the 1,000 Btu/ft3commonly associated with natural gas. The combustor requires a specified heat input to maintain performance, so a significantly higher flow rate is required for syngas than natural gas for a similar turbine size. Also, natural gas consists mainly of methane (CH4), whereas syngas consists mainly of CO and hydrogen (H2). The H2composition of the syngas results in a higher flame speed and broader flammability limits, meaning the syngas produces a stable flame at leaner conditions than natural gas and the combustion speed is much quicker than natural gas. This more rapid combustion speed limits the use of conventional natural gas combustor nitrogen oxide (NOx) control. Another complication is the relatively high concentrations of hydrogen sulfide (H2S) in syngas compared to natural gas.

To combat these issues, diluents such as nitrogen or steam are used to lower the flame temperature. The lower temperature limits the formation of NOx as the syngas is combusted. Nitrogen is an ideal solution in oxygen blown applications as it should be readily available as a by-product from the air separation unit.

There are a number of experimental and theoretical studies on the energy conversion of oil palm derivative biomass. Moreover, the potential of this abundant biomass residue for renewable energy in major producing countries in Southeast Asia has been well documented. In this study, the results of an equilibrium model of downdraft gasification of oil palm fronds (OPF), developed using the Aspen Plus chemical process simulator software, and its validation are presented. In addition, an optimization of the major output parameter of importance (i.e., the higher heating value of syngas) with respect to the main operating parameters (i.e., temperature, equivalence ratio (ER), and moisture content) was performed. The response surface method (RSM) was used to determine the mathematical relationship between the response of interest, which was the heating value of syngas, and the operating conditions. This method was used to further determine the conditions that would lead to optimum higher heating values of syngas. Optimum values identified by RSM were: oxidation zone temperature of 1000 C, moisture content in the range of 4%, and an equivalence ratio of 0.35. These optimum operating conditions and the corresponding higher heating value of syngas were found to correspond with the experimental results.

The process of gasification is relatively complicated and involves a large number of chemical and physical processes (Baruah and Baruah 2014). The gasification process takes place in four stages called drying, pyrolysis, oxidation, and reduction. A number of studies had been carried out in the past on modelling of the thermochemical conversation of various biomass materials (Muilenburg et al. 2011; Bates et al. 2016). Phenomenological models that represent the various chemical processes in each stage of gasification using mathematical relations (Muilenburg et al. 2011; Sulaiman et al. 2012; Bates et al. 2016) are more commonly applied than the black box modelling approach that use Artificial Neural Network (ANN) (Puig-Arnavat et al. 2013; Rodrigues et al. 2016). These models can be placed into two main classes: equilibrium models that assume all major reactions of pyrolysis and gasification to reach chemical equilibrium during the gasification process, and kinetic models, which involve kinetic rate equations. In the current study the equilibrium modelling approach is used, as it has been reported by many authors to satisfactorily predict the gasification process. Most of the modelling work in the literature has focused on predicting the composition of resulting syngas from the gasification process depending on values of operating conditions. Yet most of the studies do not focus on optimizing the heating value of produced syngas and determining the optimum operating conditions.

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