Influence of exhaust gas heating and L/D ratios on the discharge efficiencies for an activated carbon natural gas storage system

A transient 2D axi-symmetric and lumped parameter (LP) model with constant outflow conditions have been developed to study the discharge capacity of an activated carbon bed. The predicted discharge times and variations in bed pressure and temperature are in good agreement with experimental results obtained from a 1.82 l adsorbed natural gas (ANG) storage system. Under ambient air conditions, a maximum temperature drop of 29.5 K and 45.5 K are predicted at the bed center for discharge rates of 1.0 l min(-1) and 5.0 l min(-1) respectively. The corresponding discharge efficiencies are 77% and 71.5% respectively with discharge efficiencies improving with decreasing outflow rates. Increasing the LID ratio from 1.9 to 7.8 had only a marginal increase in the discharge efficiency. Forced convection (exhaust gas) heating had a significant effect on the discharge efficiency, leading to efficiencies as high as 92.8% at a discharge of 1.0 l min(-1) and 88.7% at 5 l min(-1). Our study shows that the LP model can be reliably used to obtain discharge times due to the uniform pressure distributions in the bed. Temperature predictions with the LP model were more accurate at ambient conditions and higher discharge rates, due to greater uniformity in bed temperatures. For the low thermal conductivity carbon porous beds, our study shows that exhaust gas heating can be used as an effective and convenient strategy to improve the discharge characteristics and performance of an ANG system. (C) 2013 Elsevier Ltd. All rights reserved.

ADAPTATION OF MW LEVEL NATURAL GAS LEAN BURN ENGINE FOR PRODUCER GAS OPERATION A GRID CONNECTED POWER PLANT

Availability of producer gas engines at MW being limited necessitates to adapt engine from natural gas operation. The present work focus on the development of necessary kit for adapting a 12 cylinder lean burn turbo-charged natural gas engine rated at 900 kWe (Waukesha make VHP5904LTD) to operate on producer and set up an appropriate capacity biomass gasification system for grid linked power generation in Thailand. The overall plant configuration had fuel processing, drying, reactor, cooling and cleaning system, water treatment, engine generator and power evacuation. The overall project is designed for evacuation of 1.5 MWe power to the state grid and had 2 gasification system with the above configuration and 3 engines. Two gasification system each designed for about 1100 kg/hr of woody biomass was connected to the engine using a producer gas carburetor for the necessary Air to fuel ratio control. In the use of PG to fuel IC engines, it has been recognized that the engine response will differ as compared to the response with conventional fueled operation due to the differences in the thermo-physical properties of PG. On fuelling a conventional engine with PG, power de-rating can be expected due to the lower calorific value (LCV), lower adiabatic flame temperature (AFT) and the lower than unity product to reactant more ratio. Further the A/F ratio for producer gas is about 1/10th that of natural gas and requires a different carburetor for engine operation. The research involved in developing a carburetor for varying load conditions. The patented carburetor is based on area ratio control, consisting of a zero pressure regulator and a separate gas and air line along with a mixing zone. The 95 litre engine at 1000 rpm has an electrical efficiency of 33.5 % with a heat input of 2.62 MW. Each engine had two carburetors designed for producer gas flow each capable of handling about 1200 m3/hr in order to provide similar engine heat input at a lower conversion efficiency. Cold flow studies simulating the engine carburetion system results showed that the A/F was maintained in the range of 1.3 +/- 0.1 over the entire flow range. Initially, the gasification system was tested using woody biomass and the gas composition was found to be CO 15 +/- 1.5 % H-2 22 +/- 2% CH4 2.2 +/- 0.5 CO2 11.25 +/- 1.4 % and rest N-2, with the calorific value in the range of 5.0 MJ/kg. After initial trials on the engine to fine tune the control system and adjust various engine operating parameter a peak load of 800 kWe was achieved, while a stable operating conditions was found to be at 750 kWe which is nearly 85 % of the natural gas rating. The specific fuel consumption was found to be 0.9 kg of biomass per kWh.

Numerical Simulation of Nox Formation in Coal Combustion with Inlet Natural Gas Burning

A full two-fluid model of reacting gas-particle flows and coal combustion is used to simulate coal combustion with and without inlet natural gas added in the inlet. The simulation results for the case without natural gas burning is in fair agreement with the experimental results reported in references. The simulation results of different natural gas adding positions indicate that the natural gas burning can form lean oxygen combustion enviroment at the combustor inlet region and the NOz concentration is reduced. The same result can be obtained from chemical equilibrium analysis.

Analysis of Temperature and Pressure Changes in Liquefied Natural Gas (LNG) Cryogenic Tanks

Liquefied natural gas (LNG) is being developed as a transportation fuel for heavy vehicles such as trucks and transit buses, to lessen the dependency on oil and to reduce greenhouse gas emissions. The LNG stations are properly designed to prevent the venting of natural gas (NG) from LNG tanks, which can cause evaporative greenhouse gas emissions and result in fluctuations of fuel flow and changes of fuel composition. Boil-off is caused by the heat added into the LNG fuel during the storage and fueling. Heat can leak into the LNG fuel through the shell of tank during the storage and through hoses and dispensers during the fueling. Gas from tanks onboard vehicles, when returned to LNG tanks, can add additional heat into the LNG fuel. A thermodynamic and heat transfer model has been developed to analyze different mechanisms of heat leak into the LNG fuel. The evolving of properties and compositions of LNG fuel inside LNG tanks is simulated. The effect of a number of buses fueled each day on the possible total fuel loss rate has been analyzed. It is found that by increasing the number of buses, fueled each day, the total fuel loss rate can be reduced significantly. It is proposed that an electric generator be used to consume the boil-off gas or a liquefier be used to re-liquefy the boiloff gas to reduce the tank pressure and eliminate fuel losses. These approaches can prevent boil-off of natural gas emissions, and reduce the costs of LNG as transportation fuel.

Monte Carlo Valuation of natural gas investments

This paper deals with the valuation of energy assets related to natural gas. In particular, we evaluate a baseload Natural Gas Combined Cycle (NGCC) power plant and an ancillary instalation, namely a Liquefied Natural Gas (LNG) facility, in a realistic setting; specifically, these investments enjoy a long useful life but require some non-negligible time to build. Then we focus on the valuation of several investment options again in a realistic setting. These include the option to invest in the power plant when there is uncertainty concerning the initial outlay, or the option's time to maturity, or the cost of CO2 emission permits, or when there is a chance to double the plant size in the future. Our model comprises three sources of risk. We consider uncertain gas prices with regard to both the current level and the long-run equilibrium level; the current electricity price is also uncertain. They all are assumed to show mean reversion. The two-factor model for natural gas price is calibrated using data from NYMEX NG futures contracts. Also, we calibrate the one-factor model for electricity price using data from the Spanish wholesale electricity market, respectively. Then we use the estimated parameter values alongside actual physical parameters from a case study to value natural gas plants. Finally, the calibrated parameters are also used in a Monte Carlo simulation framework to evaluate several American-type options to invest in these energy assets. We accomplish this by following the least squares MC approach.

Simulation of Natural Gas Production in Hydrate Reservoirs

This paper simulates a one-dimensional physical model of natural gas production from hydrate dissociation in a reservoir by depressurization. According to the principles of solid hydrate decomposition in stratum and flow of natural gas in porous medium, the pressure governing equations for both gas zone and hydrate zone are set up based on the physical production model. Using the approximation reported by N. N. Verigin et al. (1980), the nonlinear governing equations are simplified and the self-similar solutions are obtained. Through calculation, for different reservoir parameters, the distribution characters of pressure are analyzed. The decline trend of natural gas production rate with time is also studied. The simulation results show that production of natural gas from a hydrate reservoir is very sensitive to several reservoir parameters, such as wellbore pressure and stratum porosity and permeability.

Avaliação de Correlações e Equações de Estado para Determinação de Fatores de Compressibilidade de Gás Natural

O fator de compressibilidade (Z) de gás natural é utilizado em vários cálculos na engenharia de petróleo (avaliação de formações, perda de carga em tubulações, gradiente de pressão em poços de gás, cálculos de balanço de massa, medição de gás, compressão e processamento de gás). As fontes mais comuns de valores de Z são medições experimentais, caras e demoradas. Essa propriedade também é estimada por correlações empíricas, modelos baseados no princípio dos estados correspondentes ou equações de estado (EOS). Foram avaliadas as capacidades das EOS de Soave-Redlich-Kwong (SRK), Peng-Robinson (PR), Patel-Teja (PT), Patel-Teja-Valderrama (PTV), Schmidt-Wenzel (SW), Lawal-Lake-Silberberg (LLS) e AGA-8 para previsão desta propriedade em aproximadamente 2200 pontos de dados experimentais. Estes pontos foram divididos em quatro grupos: Grupo 1 (Presença de frações C7+, Grupo 2 (temperaturas inferiores a 258,15 K), Grupo 3 (pressões superiores a 10000 kPa) e Grupo 4 (pressões inferiores a 10000 kPa). Os cálculos utilizando as equações de estado sob diferentes esquemas de previsão de coeficientes binários de interação foram cuidadosamente investigados. Os resultados sugerem que a EOS AGA-8 apresenta os menores erros para pressões de até 70000 kPa. Entretanto, observou-se uma tendência de aumento nos desvios médios absolutos em função das concentrações de CO2 e H2S. As EOS PTV e a EOS SW são capazes de predizer o fator de compressibilidade (Z) com desvios médios absolutos entre os valores calculados e experimentais com precisão satisfatória para a maioria das aplicações, para uma variada faixa de temperatura e pressão. Este estudo também apresenta uma avaliação de 224 métodos de cálculo de Z onde foram utilizadas 8 correlações combinadas com 4 regras de mistura para estimativa de temperaturas e pressões pseudorreduzidas das amostras, junto com 7 métodos de caracterização das propriedades críticas da fração C7+, quando presente na composição do gás. Em função dos resultados são sugeridas, para diferentes tipos de sistemas, as melhores combinações de correlações com regras de mistura capazes de predizer fatores de compressibilidade (Z) com os menores erros absolutos médios relativos

Do oil and gas platforms off California reduce recruitment of bocaccio (Sebastes paucispinis) to natural habitat? An analysis based on trajectories derived from high-frequency radar

To investigate the possibility that oil and gas platforms may reduce recruitment of rockfishes (Sebastes spp.) to natural habitat, we simulated drift pathways termed “trajectories” in our model) from an existing oil platform to nearshore habitat using current measurements from high-frequency (HF) radars. The trajectories originated at Platform Irene, located west of Point Conception, California, during two recruiting seasons for bocaccio (Sebastes paucispinis): May through August, 1999 and 2002. Given that pelagic juvenile bocaccio dwell near the surface, the trajectories estimate transport to habitat. We assumed that appropriate shallow water juvenile habitat exists inshore of the 50-m isobath. Results from 1999 indicated that 10% of the trajectories represent transport to habitat, whereas 76% represent transport across the offshore boundary. For 2002, 24% represent transport to habitat, and 69% represent transport across the offshore boundary. Remaining trajectories (14% and 7% for 1999 and 2002, respectively) exited the coverage area either northward or southward along isobaths. Deployments of actual drifters (with 1-m drogues) from a previous multiyear study provided measurements originating near Platform Irene from May through August. All but a few of the drifters moved offshore, as was also shown with the HF radar-derived trajectories. These results indicate that most juvenile bocaccio settling on the platform would otherwise have been transported offshore and perished in the absence of a platform. However, these results do not account for the swimming behavior of juvenile bocaccio, about which little is known.

Modelagem e simulação da formação de hidrocarbonetos na combustão do gás natural

A exaustão de um veículo de motor a diesel é uma importante fonte de poluentes atmosféricos, pois forma uma matriz complexa composta de poluentes regulados e não regulados pelos órgãos governamentais. Dentre os poluentes regulados podemos citar óxidos de nitrogênio (NOx) e material particulado. Os poluentes não regulados são pouco estudados até hoje e dentre estes encontra-se a classe dos hidrocarbonetos policíclicos aromáticos e seus derivados nitrados (nitro-HPA). Estes são encontrados na exaustão do diesel na forma gasosa ou agregados ao material particulado. Hoje, o interesse em estudos destes compostos vem aumentando, devido às suas atividades carcinogênicas e mutagênicas às quais estão sujeitas as populações dos centros urbanos. O impacto causado pelos nitro-HPA emitidos por motores a ciclo diesel ao ambiente não está ainda completamente estabelecido. Este estudo consiste na modelagem e simulação do processo de combustão de hidrocarbonetos na faixa de C1 a C4 com o objetivo de descrever a formação de compostos aromáticos, principalmente HPA, e óxidos de nitrogênio a partir de modelos cinéticos de combustão propostos na literatura como referência e fazendo uso do software de simulação Kintecus. Este projeto tem como objetivo em longo prazo propor um modelo cinético para combustão do óleo Diesel. Foi iniciada a construção de um modelo cinético de combustão a partir de modelos de hidrocarbonetos simples de C1 a C4, com formação de aromáticos, HPA e óxidos de nitrogênio. Os modelos originais foram avaliados e modificados a fim de estudar como parâmetros do modelo afetam a concentração das espécies de interesse. Foi observado a tendência de formação de benzeno e fulveno em baixas temperaturas e a tendência de formação de antraceno, pireno, fenantreno a temperaturas mais altas. Foi avaliado que a conversão NO-NO2 ocorre em maiores proporções em reações iniciadas a baixas temperaturas, 600 K. Os resultados indicam que propano é o maior responsável por esta conversão. O modelo final obtido resultou da união dos modelos de combustão Hori e Marinov mais inclusão do GRI-Mech 3.0 e reações adicionais de NOx retiradas da base de dados NIST