Firing Natural Gas Research Articles

Assessment of the potential for conversion of TP-108 boilers to firing natural gas and fuel oil

TP-108 boilers were initially designed to burn milled peat. In the 1980s, they were reconstructed for conversion to burning natural gas as well. However, operation of these boilers revealed problems due to low reheat temperature and great air inleakage in the furnace. The initial design of the boiler and its subsequent reconstruction are described in the paper. Measures are presented for further modernization of TP-108 boilers to eliminate the above-mentioned problems and enable natural gas or fuel oil only to be burned in them. Thermal design calculations made using a specially developed adapted model (AM) suggest that replacement of the existing burners with new oil/gas burners, installation of steam-to-steam heat exchangers (SSHE), and sealing of the boiler gas path to make it gas tight will allow the parameters typical of gas-and-oil fired boilers to be attained. It is demonstrated that SSHEs can yield the design secondary steam reheat temperature, although this solution is not typical for natural circulation boilers with steam reheat. The boiler equipped with SSHEs can operate on fuel oil or natural gas with flue gas recirculation or without it. Moreover, operation of the boiler with flue gas recirculation to the air duct in combination with staged combustion enables the required environmental indicators to be attained.

Effect of full-bore natural gas release on fire and individual risks: A case study for an LNG-Fueled ship

This study investigated the significance of categorizing and selecting representative leak sizes in Quantitative Risk Assessment (QRA) for estimating natural gas fire risks. In most fire QRA procedures, the full-bore sizes of leaks have been overlooked even though they causes the catastrophic consequences with relatively high frequencies. So, in the present study, the effect of particular leak sizes on the individual risks (IRs) were investigated through the fire risk assessment. As case studies, LNG (Liquefied Natural Gas) fuel gas supply system for a large ship were considered with three different approaches. Approach 1 considers only three categories of leak sizes; small, medium, and large. Approach 2 includes the full-bore leak in addition to categories of Approach 1, and Approach 3 reflects more categories of leak sizes with every 1 mm increment in diameter. Compared with the total IR of Approach 3, the total IR of Approach 1 was two times lower, whereas Approach 2 resulted in the comparable total IR with an approximately 4% deviation. Admitting that Approach 3 should be close to the exact solution, Approach 2 gave acceptable results, whereas Approach 1 unsatisfactorily underestimated the total IR. The results indicated that full-bore leak accidents are critically important scenarios and omission of them can lead to misjudgment in the risk-informed decision-making process. Taking the full-bore accidents into additional account to the conventional simplified QRA can reduce the time and effort for estimating the leak-related risks without a significant loss of accuracy in the estimated risks.

A Thermodynamic Model of Solar Thermal Energy Assisted Natural Gas Fired Combined Cycle (NGCC) Power Plant

A solar thermal energy assisted NGCC power plant was modeled to investigate the impact on plant efficiency, output and CO2 emission with solar thermal energy addition. In this particular model, with 23.7 MWth solar thermal energy input to the HRSG, the duct firing could be shut off, 2337.5 kg/h natural gas would be saved, and 6.2 t/hr CO2 emission would be eliminated. However, there would also be a 4.07 MWe loss in power from the combined cycle. Another solar input approach shows 14.35 MWe additional electricity would be generated with 35 MWth solar thermal energy addition. The thermodynamic analyses in this paper demonstrated the possibilities to utilize the solar thermal energy to reduce fuel consumption and CO2 emission, or to increase the NGCC power plant efficiency and output, while taking advantage of the already existing power plant infrastructure.

Characteristics of syngas reburning in a natural gas firing furnace - Effects of combustible gas species in the syngas

Co-firing of synthesis gas (syngas) produced from biomass/waste gasification is a promising option for increasing renewable energy production from existing boilers burning fossil fuels. This study presents an experimental approach to utilizing syngas as reburn fuel for NOx emissions reduction. In a 65 kWth furnace firing natural gas, the reburning characteristics for simulated syngas representing main syngas components, such as CH4, CO and H2, were evaluated for co-firing ratios up to 20%. The heating value and gas residence time of the syngas were maintained in the reburn zone by adjusting the N2 concentration. Detailed distribution of temperature, O2 and NOx concentrations within the furnace were measured for the test conditions. The lower stoichiometric ratios of the primary combustion zone by reburning were favorable in reducing NOx formation from the main fuel. Among the syngas components, CH4 was most efficient, exhibiting an immediate decrease in NOx concentration after injection through the formation of HCN. CO and H2 also contributed to the reduction of NOx emissions by suppressing further formation of NOx in the reburn zone. The NOx removal efficiency was diminished by an increase in NOx concentrations in the burnout zone.

Sequential supplementary firing in natural gas combined cycle with carbon capture: A technology option for Mexico for low-carbon electricity generation and CO2 enhanced oil recovery

Combined cycle gas turbine power plants with sequential supplementary firing in the heat recovery steam generator could be an attractive alternative for markets with access to competitive natural gas prices, with an emphasis on capital cost reduction, and where supply of carbon dioxide for Enhanced Oil Recovery (EOR) is important. Sequential combustion makes use of the excess oxygen in gas turbine exhaust gas to generate additional CO2, but, unlike in conventional supplementary firing, allows keeping gas temperatures in the heat recovery steam generator below 820°C, avoiding a step change in capital costs. It marginally decreases relative energy requirements for solvent regeneration and amine degradation. Power plant models integrated with capture and compression process models of Sequential Supplementary Firing Combined Cycle (SSFCC) gas-fired units show that the efficiency penalty is 8.2% points LHV compared to a conventional natural gas combined cycle power plant with the same capture technology. The marginal thermal efficiency of natural gas firing in the heat recovery steam generator can increase with supercritical steam generation to reduce the efficiency penalty to 5.7% points LHV. Although the efficiency is lower than the conventional configuration, the increment in the power output of the combined steam cycle leads a reduction of the number of gas turbines, at a similar power output to that of a conventional natural gas combined cycle. This has a positive impact on the number of absorbers and the capital costs of the post combustion capture plant by reducing the total volume of flue gas by half on a normalised basis. The relative reduction of overall capital costs is, respectively, 15.3% and 9.1% for the subcritical and the supercritical combined cycle configurations with capture compared to a conventional configuration. For a gas price of $2/MMBTU, the Total Revenue Requirement (TRR) – a metric combining levelised cost of electricity and revenue from EOR – of subcritical and supercritical sequential supplementary firing is consistently lower than that of a conventional NGCC by, respectively, 2.2 and 5.7 $/MWh at 0 $/t CO2 and by 4.9 and 6.7 $/MWh at $50/t CO2. At a gas price of $4/MMBTU and $6/MMBTU, the TRR of a subcritical configuration is consistently lower for any carbon selling price higher than 2.5 $/t CO2 and 37 $/t CO2 respectively.

Effects of nitrogen dilution on the NOx and CO emission of H2/CO/CH4 syngases in a partially-premixed gas turbine model combustor

In this study, the nitrogen dilution effect in H2/CO/CH4 syngas flames on the characteristics of NOx and CO emissions were investigated in a partially premixed gas turbine model combustor. Nitrogen was diluted into the fuel side and combustor liner temperature, and the flame structures were observed in order to find information that was critical for analyzing the results of the NOx and CO emissions. The addition of nonflammable N2 was effective in decreasing the combustion temperature, which was attributed to the reduction in the reaction rate of syngas oxidation as well as the increase in the overall heat capacity of the air-fuel mixture at a constant heat input. NOx suppression was successfully achieved up to the one digit ppmv level for all heat input and all fuel composition by the 60%-fuel side dilution of nitrogen. However, increases in nitrogen dilution increased the possibility of CO emission; therefore, extremely high CO was emitted in a 100%-CO flame at a low load with 60%-nitrogen dilution reaching 10,000 ppmv. The dilution of nitrogen in syngas considerably changed the flame structure, such as flame length, thickness, angle, location, and intensity. These flame structures provided valuable clues for the analysis of the NOx and CO emission results in relation to the flame temperature results. Based on the integration of the test results, a cause-and-effect diagram of NOx and CO emissions was plotted, and the root causes of NOx suppression were determined to be the decreases in both temperature and residence time in the hot combustion zone, and the critical path of these root causes was clarified. Although the nitrogen dilution technique has been investigated in detail, and the effects are fully understood, the careful monitoring of CO and flame detachment from the fuel nozzle is recommended when applying the nitrogen dilution technique to reduce NOx emission, especially in cases of low load operation. A practical dataset was collected from the combustion test at gas turbine relevant conditions for a wide range of fuel compositions. These results and the knowledge gained from this study could be usefully applied for the environmentally friendly and safe operation of integrated gasification combined cycle and synthetic natural gas firing gas turbine power plants.

Temperature Distribution Analysis on Syngas Combustion in Microgas Turbine

Gas turbines are capable to utlize variety of fuel including natural gas, fuel oils and synthetic gas. It has environmental advantages and thus gas turbines are favourable in the power generating industries. The use of synthetic gas or syngas may reduce the CO2 and NOx emissions. The efficiency of syngas is comparable with natural gas. With the current constrain on the environmental issues, the use of syngas in gas turbines has been increasing. Despite its many advantages, the study on the combustion characteristics still remains a challenge, due to its variety fuel components. This paper aims to discuss the CFD analysis on the flame and flue gas temperature distribution in a full scale microgas turbine operating on syngas. Three cases were simulated with variety of natural gas concentration. A base case firing natural gas (100% methane) was first established using actual operation. Validation on the combustion model is made by comparing the flame temperature distribution of methane with reasonable accuracy. Simulation results with syngas show similar flame temperature distribution as natural gas combustion. The average temperature is much dependent on the composition of methane in syngas. The highest temperature given by syngas is made from the highest methane composiotion.

シンポジウム「LNGを燃料とする主機関の機関室の構成機器全般について」の司会をして

シンポジウム「LNGを燃料とする主機関の機関室の構成機器全般について」の司会をして

「LNGを燃料とする主機関の機関室の構成機器全般について」の特集号によせて

「LNGを燃料とする主機関の機関室の構成機器全般について」の特集号によせて

A high-temperature gas-and-steam turbine plant operating on combined fuel

A high-temperature gas–steam turbine plant (GSTP) for ultrasupercritical steam conditions is proposed based on an analysis of prospects for the development of power engineering around the world and in Russia up to 2040. The performance indicators of a GSTP using steam from a coal-fired boiler with a temperature of 560–620°C with its superheating to 1000–1500°C by firing natural gas with oxygen in a mixingtype steam superheater are analyzed. The thermal process circuit and design of a GSTP for a capacity of 25 MW with the high- and intermediate-pressure high-temperature parts with the total efficiency equal to 51.7% and the natural gas utilization efficiency equal to 64–68% are developed. The principles of designing and the design arrangement of a 300 MW GSTP are developed. The effect of economic parameters (the level and ratio of prices for solid fuel and gas, and capital investments) on the net cost of electric energy is determined. The net cost of electric energy produced by the GSTP is lower than that produced by modern combined-cycle power plants in a wide variation range of these parameters. The components of a high-temperature GSTP the development of which determines the main features of such installations are pointed out: a chamber for combusting natural gas and oxygen in a mixture with steam, a vacuum device for condensing steam with a high content of nondensables, and a control system. The possibility of using domestically available gas turbine technologies for developing the GSTP’s intermediate-pressure high-temperature part is pointed out. In regard of its environmental characteristics, the GSTP is more advantageous as compared with modern condensing power plants: it allows a flow of concentrated carbon dioxide to be obtained at its outlet, which can be reclaimed; in addition, this plant requires half as much consumption of fresh water.

Numerical Investigation on the Effect of Using Mixtures of Natural Gas and Aviation Fuel on Flame Characteristics of Swirl Gas Turbine Combustor

The present paper is directed to study aviation fuel combustion compared to that of natural gas in a gas turbine swirl Combustor. Finite-volume based CFD commercial package ANSYS Fluent 12 is used for the present investigation. The SST k-ω model is used to simulate turbulence. The non-premixed combustion model is used to simulate the reacting flow. Combustion of natural gas is sooty in nature. Thus, soot distribution in the combustor is investigated numerically using the two step soot model. Simple expressions for the soot formation and oxidation rates were employed. The radiation heat transfer equation was solved using the P-1 radiation model. The formation of thermal NO from molecular nitrogen was modeled and the prompt NO was also included in the computations. CFD modeling is validated against experimental temperature measurements for a swirl combustor when firing natural gas as referred to a previous paper. Using the SST-K-ω for predicting gas temperature distributions satisfy reasonable agreement with the experimental temperature measurements, except near the combustor upstream and in the vicinity of the combustor axis.

Thermodynamic Analysis of a Power Plant Integrated with Fogging Inlet Cooling and a Biomass Gasification

Biomass energy and especially biofuels produced by biomass gasification are clean and renewable options for power plants. Also, on hot days the performance of gas turbines decreases substantially, a problem that can be mitigated by fog cooling. In the present paper, a biomass-integrated fogging steam injected gas turbine cycle is analyzed with energy and exergy methods. It is observed that (1) increasing the compressor pressure ratio raises the air flow rate in the plant but reduces the biomass flow rate; (2) increasing the gas turbine inlet temperature decreases the air and biomass flow rates; (3) increasing the compressor pressure ratio raises the energy and exergy efficiencies, especially at lower pressure ratios; (4) increasing the gas turbine inlet temperature raises both efficiencies; and (5) overspray increases the energy efficiency and net cycle power slightly. The gas turbine exhibits the highest exergy efficiency of the cycle components and the combustor the lowest. A comparison of the cycle with similar cycles fired by natural gas and differently configured cycles fueled by biomass shows that the cycle with natural gas firing has an energy efficiency 18 percentage points above the biomass fired cycle, and that steam injection increases the energy efficiency about five percentage points relative to the cycle without steam injection. Also, the influence of steam injection on energy efficiency is more significant than fog cooling.

From Coal to Natural Gas: Its impact on Kiln Production, Clinker Quality and Emissions

In the North American energy market, natural gas (NG) prices have been gradually decreasing during the past several years, primarily due to advances in shale gas extraction techniques. The availability of cheaper NG, while seen as an attractive short-term fuel switching option, is viewed with caution by most cement plants due to long-term procurement concerns. Also, due to traditionally higher NG prices, cement plants have invested heavily into solid fuels, including storage, grinding, handling, and dosing systems—often achieving high thermal substitution rates (TSRs) of solid alternative fuels and raw materials (AFRs). As a result, a wealth of knowledge has been acquired on firing solid fuels, including some of the more difficult ones, e.g., higher sulfur petcoke and bigger size AFRs, where operational issues such as build-ups, emissions, and production losses have been and are being minimized. Switching to gas firing, however, requires readaptation of combustion and process guidelines for a fuel which, although in principal, is easier to burn, but has relatively lower radiative heat transfer and sharper burning characteristics than coal. As such, the plants, which have switched to NG firing, have observed inconsistent trends in production, energy, and emission performance, mainly due to the lack of sufficient information on combustion/process interactions of the two fuel types required for cost-effective optimization. An NG flame ignites earlier, releases intense heat but lacks dissipation of heat as compared with a solid fuel flame, thereby requires plant specific adjustments. This paper presents actual results of NG firing trials at selected cement plants along with mineral interactive computational fluid dynamics (MI-CFD) predictions, subsequent to validation from the plant data, on four kiln and four calciners. Recommendations are also made to improve and optimize NG firing by taking into considerations of the combustion and mineral interactions.

An Application Analysis of Solution Circulation Heat Recovery System in Natural Gas Fired Boiler

In this paper, a new system which absorbs the water vapor in flue gas of natural gas fired boiler (NGFB) by desiccant solution is introduced. This system can recover the latent heat of water vapor and improve the thermal efficiency of the NGFB significantly. In the theoretical analysis, the packed tower which is the most important equipment of solution circulation heat recovery system (SCHRS) can be designed by establishing a mathematical model. Based on the recovery efficiency of water vapor by desiccant solution absorption, the thermal efficiency analysis of NGFB is discussed, which show that SCHRS has a good application prospect in NGFB waste heat recovery.

Uncertainty of the allocation factors of heat and electricity production of combined cycle power plant

There are many different methods for the allocation of CO2 emissions in Combined Heat and Power plants. The choice of allocation method has a great effect on energy pricing and CO2 allocation in Combined Heat and Power plants. The power bonus method is the main method used for the allocation of CO2 emissions between heat and power production in the European Union and given as a standard. Aside from this method, six different allocation methods were tested on the Combined Cycle Power Plant in this study. Operational and design parameters of the Combined Cycle Power Plant were taken into consideration during analysis. The District Heating system, with an annual heat load of 27 GWh and maximum heat effect requirement of 14 MW, was chosen for the simulation model. This load was represented by the university campus. The energy source for District Heating was a Combined Cycle Power Plant with supplementary firing technology and natural gas as a fuel. The modeling of the system was carried out by the simulation software Aspen HYSYS, while data post-processing was done by MATLAB. Sensitivity analysis of the different allocation methods was performed for the Combined Cycle Power Plant under a yearly heat and electricity load. It was noted that different allocation methods produce different allocation factors. The differences between heat allocation factors for design and operational conditions were small. The most sensitive method was the power bonus method. The study showed that the decision regarding allocation method should be carefully analyzed before implementation in the standards and different policies, because benefits from cogeneration technology and distribution systems should be enabled. The results obtained in this study can be used by designers of Combined Heat and Power systems and policy makers, as a tool for developing an emission trading system for Combined Heat and Power plants and for the pricing of heat and power.

Development of Natural Gas Fired Combined Cycle Plant for Tri-Generation of Power, Cooling and Clean Water Using Waste Heat Recovery: Techno-Economic Analysis

Tri-generation is one of the most efficient ways for maximizing the utilization of available energy. Utilization of waste heat (flue gases) liberated by the Al-Hamra gas turbine power plant is analyzed in this research work for simultaneous production of: (a) electricity by combining steam rankine cycle using heat recovery steam generator (HRSG); (b) clean water by air gap membrane distillation (AGMD) plant; and (c) cooling by single stage vapor absorption chiller (VAC). The flue gases liberated from the gas turbine power cycle is the prime source of energy for the tri-generation system. The heat recovered from condenser of steam cycle and excess heat available at the flue gases are utilized to drive cooling and desalination cycles which are optimized based on the cooling energy demands of the villas. Economic and environmental benefits of the tri-generation system in terms of cost savings and reduction in carbon emissions were analyzed. Energy efficiency of about 82%–85% is achieved by the tri-generation system compared to 50%–52% for combined cycles. Normalized carbon dioxide emission per MW·h is reduced by 51.5% by implementation of waste heat recovery tri-generation system. The tri-generation system has a payback period of 1.38 years with cumulative net present value of $66 million over the project life time.

Microstructure and creep behaviour of pressure boundary welds from Grade 91 steel tee

New power generation equipment firing either coal or natural gas is required to operate at high levels of efficiency with greater operational flexibility than has been true for such equipment in the past. Because of their unique combination of superior creep strength and favourable thermal–physical properties, Grade 91 and the other creep strength enhanced ferritic (CSEF) steels are materials of choice for components operating in the elevated temperature sections of this equipment. To fully realise the benefits of these alloys, it is essential that careful control be maintained during all phases of processing of the material, from design, through material production, to fabrication and installation. Absent such control, rates of damage accumulation can be much greater than expected from ‘Code’ minimum data. Problems have been associated with incorrect heat treatment: failure to develop the necessary structure during the normalising heat treatment or breakdown of that structure during subsequent sub-critical heat treatments. Heat treating schedules must consider not only the specific chemical composition of the base and weld filler metal, but also the cumulative impact of multiple heat treatments on the final material structure and its properties. The present work has examined the performance of welds in an ex-service component. The results suggest that, even when less than optimal heat treatment is carried out, the susceptibility for Type IV cracking in weld heat affected zones may be the life limiting factor for most CSEF steel components.

Burns in Tehran: demographic, etiological, and clinical trends

Abstract Background: Burns are a major public health problem. They often require intensive care and long periods of hospitalization. In Tehran, about 5% of all hospitalized injuries are burns. There are no published long-term epidemiological studies regarding burn injuries of adults in Iran. Objective: To identify risk factors for burn injuries and provide a starting point for the establishment of an effective prevention plan. Methods: We analyzed the demographic, etiological, and clinical data of 1860 burn patients admitted to a major acute care hospital in Tehran between March 2010 and April 2011. Data were obtained from the registry recorded in Shahid Motahari Trauma Hospital and evaluated using a chi-square test. Results: Males were more than twice as likely to be burn patients than females (72.0% vs. 28.0%). Second and third-degree burns with a body surface area of 21%-30% constituted the highest injury reported (75.3%). The most common causes of the recorded burns were natural gas, gasoline (42%) and open fire (10.2%). Unintentional burns were reported in 85% of the cases, and 15% of the burn victims were suicide-related incidents; mainly among women. In 75% of suicide attempts, women set themselves on fire to commit suicide. The mean duration of hospitalization was 25 days and the mortality rate was 10.7%. Mean age of reported deaths was 38.6 years; with a mean of 30 years among women and 51.5 years among men. Conclusion: The group at highest risk was young men 21-30 years old. However, an astonishing finding was that 75% of suicidal-related incidents involved women setting themselves on fire. Those with the highest mortality rate were victims of burns with gas, gasoline, and kerosene; with a mean age of 30 years of death among women.

Energetic Evaluation of Different Flow Sheet Modifications of Post-Combustion CO2 Capture Plant at Coal and Natural Gas Fired Power Plant for a Generic Improved Solvent

Abstract The post-combustion capture (PCC) technology is a promising possibility to reduce CO 2 emissions of fossil fuel fired power plants. One of the main concerns for the PCC is the loss in electric power output. A reduction in efficiency penalty for solvent based PCC can be achieved by improving the solvent properties as well as by improving the process design. There are many different process flow sheet modifications with an improvement in process design reported in literature. In this work two of these modifications for a capture plant are evaluated. To be able to compare these process modifications it is necessary to evaluate them on identical solvent and process conditions. The modified processes are compared to base cases processing the flue gas from a supercritical pulverised coal fired power plant as well as a natural gas combined cycle power plant. The solvent used in the capture plant is a generic improved solvent, representing possible future solvents. The main advantages of the flow sheet modifications are pointed out. Subsequent, the specific reboiler heat duty, the specific cooling duty and the specific auxiliary power for the capture plant are shown for the flow sheet modifications. The overall efficiency penalties for the flow sheet modifications are compared and differences are highlighted.

Competitiveness of Wind Power with the Conventional Thermal Power Plants Using Oil and Natural Gas as Fuel in Pakistan

The fossil fuels mainly imported oil and natural gas are major sources of electricity generation in Pakistan. The combustion of fossil fuels in thermal power plants has greater environmental impacts like air pollution and global warming. Additionally, the import of oil is a heavy burden on the poor economy of the country. Pakistan is a country with huge renewable sources; wind energy being the major one. This paper elucidate the cost-competitiveness of wind power with the conventional thermal power plants. In this regard, Levelized estimated cost of a 15MW wind power plant is compared with three types of conventional thermal power plants, namely (i) Oil-fired thermal power plant (ii) Natural gas-fire combine cycle power plant (iii) Diesel oil- fired gas turbine cycle 100MW each. The results show that the cost of wind energy is lowest with Rs. 3/kWh. It is concluded that the wind power is cost-competitive to the conventional thermal power plants in Pakistan. The cost estimation for wind energy is lowest of all others with Rs. 3/kWh.