Performance evaluation of premixed burner fueled with biomass derived producer gas

Energy consumption of liquefied petroleum gas (LPG) in ceramic firing process accounts for about 15–40% of production cost. Biomass derived producer gas may be used to replace LPG. In this work, a premixed burner originally designed for LPG was modified for producer gas. Its thermal performance in terms of axial and radial flame temperature distribution, thermal efficiency and emissions was investigated. The experiment was conducted at various gas production rates with equivalence ratios between 0.8 and 1.2. Flame temperatures of over 1200 °C can be achieved, with maximum value of 1260 °C. It was also shown that the burner can be operated at 30.5–39.4 kWth with thermal efficiency in the range of 84 – 91%. The maximum efficiency of this burner was obtained at producer gas flow rate of 24.3 Nm3/h and equivalence ratio of 0.84

Reduction Kinetics of 3-Hydroxybenzoate 6-Hydroxylase from Rhodococcus jostii RHA1

3-Hydroxybenzoate 6-hydroxylase (3HB6H) from Rhodococcus jostii RHA1 is a nicotinamide adenine dinucleotide (NADH)-specific flavoprotein monooxygenase involved in microbial aromatic degradation. The enzyme catalyzes the para hydroxylation of 3-hydroxybenzoate (3-HB) to 2,5-dihydroxybenzoate (2,5-DHB), the ring-fission fuel of the gentisate pathway. In this study, the kinetics of reduction of the enzyme-bound flavin by NADH was investigated at pH 8.0 using a stopped-flow spectrophotometer, and the data were analyzed comprehensively according to kinetic derivations and simulations. Observed rate constants for reduction of the free enzyme by NADH under anaerobic conditions were linearly dependent on NADH concentrations, consistent with a one-step irreversible reduction model with a bimolecular rate constant of 43 ± 2 M–1 s–1. In the presence of 3-HB, observed rate constants for flavin reduction were hyperbolically dependent on NADH concentrations and approached a limiting value of 48 ± 2 s–1. At saturating concentrations of NADH (10 mM) and 3-HB (10 mM), the reduction rate constant is 51 s–1, whereas without 3-HB, the rate constant is 0.43 s–1 at a similar NADH concentration. A similar stimulation of flavin reduction was found for the enzyme–product (2,5-DHB) complex, with a rate constant of 45 ± 2 s–1. The rate enhancement induced by aromatic ligands is not due to a thermodynamic driving force because Em0 for the enzyme–substrate complex is -179 ± 1 mV compared to an Em0 of -175 ± 2 mV for the free enzyme. It is proposed that the reduction mechanism of 3HB6H involves an isomerization of the initial enzyme–ligand complex to a fully activated form before flavin reduction takes plac

Kinetics of a Two-Component p-Hydroxyphenylacetate Hydroxylase Explain How Reduced Flavin Is Transferred from the Reductase to the Oxygenase

p-Hydroxyphenylacetate hydroxylase (HPAH) from 'Acinetobacter baumannii' catalyzes the hydroxylation of p-hydroxyphenylacetate (HPA) to form 3,4-dihydroxyphenylacetate (DHPA). HPAH is composed of two proteins:  a flavin mononucleotide (FMN) reductase (C₁) and an oxygenase (C₂). C₁ catalyzes the reduction of FMN by NADH to generate reduced FMN (FMNH-) for use by C₂ in the hydroxylation reaction. C₁ is unique among the flavin reductases in that the substrate HPA stimulates the rates of both the reduction of FMN and release of FMNH- from the enzyme. This study quantitatively shows the kinetics of how the C₁-bound FMN can be reduced and released to be used efficiently as the substrate for the C₂ reaction; additional FMN is not necessary. Reactions in which O₂ is rapidly mixed with solutions containing C₁-FMNH- and C₂ are very similar to those in which solutions containing O₂ are mixed with one containing the C₂-FMNH- complex. This suggests that in a mixture of the two proteins FMNH- binds more tightly to C₂ and has already been completely transferred to C₂ before it reacts with oxygen. Rate constants for the transfer of FMNH- from C₁ to C₂ were found to be 0.35 and ≥74 s⁻¹ in the absence and presence of HPA, respectively. The reduction of cytochrome c by FMNH- was also used to measure the dissociation rate of FMNH- from C₁. In the absence of HPA, FMNH- dissociates from C1 at 0.35 s⁻¹, while with HPA present it dissociates at 80 s⁻¹; these are the same rates as those for the transfer from C₁ to C₂. Therefore, the dissociation of FMNH- from C₁ is rate-limiting in the intermolecular transfer of FMNH- from C₁ to C₂, and this process is regulated by the presence of HPA. This regulation avoids the production of H₂O₂ in the absence of HPA. Our findings indicate that no protein-protein interactions between C₁ and C₂ are necessary for efficient transfer of FMNH- between the proteins; transfer can occur by a rapid-diffusion process, with the rate-limiting step being the release of FMNH- from C₁