Gas Production Process Research Articles

Gas production and migration in landfills and geological materials

Landfill gas, originating from the anaerobic biodegradation of the organic content of waste, consists mainly of methane and carbon dioxide, with traces of volatile organic compounds. Pressure, concentration and temperature gradients that develop within the landfill result in gas emissions to the atmosphere and in lateral migration through the surrounding soils. Environmental and safety issues associated with the landfill gas require control of off-site gas migration. The numerical model TOUGH2-LGM (Transport of Unsaturated Groundwater and Heat-Landfill Gas Migration) has been developed to simulate landfill gas production and migration processes within and beyond landfill boundaries. The model is derived from the general non-isothermal multiphase flow simulator TOUGH2, to which a new equation of state module is added. It simulates the migration of five components in partially saturated media: four fluid components (water, atmospheric air, methane and carbon dioxide) and one energy component (heat). The four fluid components are present in both the gas and liquid phases. The model incorporates gas–liquid partitioning of all fluid components by means of dissolution and volatilization. In addition to advection in the gas and liquid phase, multi-component diffusion is simulated in the gas phase. The landfill gas production rate is proportional to the organic substrate and is modeled as an exponentially decreasing function of time. The model is applied to the Montreal's CESM landfill site, which is located in a former limestone rock quarry. Existing data were used to characterize hydraulic properties of the waste and the limestone. Gas recovery data at the site were used to define the gas production model. Simulations in one and two dimensions are presented to investigate gas production and migration in the landfill, and in the surrounding limestone. The effects of a gas recovery well and landfill cover on gas migration are also discussed.

Reducing Carbon Dioxide Emissions with Enhanced Oil Recovery Projects: A Life Cycle Assessment Approach

A wide range of industries are investigating methods of reducing their emissions of greenhouse gases, such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Several options have been identified ranging from energy efficiency and reforestation to capture and storage in oceans, aquifers, or underground. Although greenhouse gases are not yet regulated, the power generation and petroleum industries are already considering greenhouse gas capture and storage methods to reduce their emissions to the atmosphere. Preferred options are the ones utilizing CO2 as a product and therefore providing an additional economic benefit to the oil and gas production process. Currently, CO2 is widely used for enhanced oil recovery (EOR) projects to extract more oil out of aging reservoirs. Thus, storage of CO2 in active reservoirs does not require technology advances and offers the advantage of reducing greenhouse gas emissions to the atmosphere. The present research conducted a life cycle assessment to determine the benefits derived from storing CO2 in active reservoirs while enhancing the extraction of oil and the impacts on the environment over the process lifetime. The potential for CO2 storage in a specific oil reservoir in Texas was demonstrated, as well as the mass balance of greenhouse gas emissions generated from the energy-intensive process. Our findings suggest that the storage capacity of this reservoir is huge, the process emissions are minimal in comparison, and the EOR activity is almost carbon-neutral when comparing net storage potential and gasoline emissions from the additional oil extracted.

Volume reduction of produced water generated from natural gas production process using membrane technology

This paper presents a case study of a natural gas production site covering various technical issues related to selection of an appropriate Reverse Osmosis (RO) system. The long-term field experience indicates the necessity of the selection of appropriate pretreatment systems for fouling-free RO operational conditions. The produced water has a variety of impurities such as oil and grease, process chemicals used for corrosion and scaling control, and dehydration of natural gas, etc. This situation leads to a complicated and extremely difficult task for a membrane specialist to design RO systems, especially the pre-treatment section. Here as part of the pretreatment selection, two types of UF membrane modules viz. spiral wound and hollow fibre, with MWCO of 8000 and 50,000 Dalton respectively, were tested in parallel with NF membranes of the spiral wound type with MWCO 200 Dalton. The UF permeate is used as feed for RO compatibility testing. Both configurations of UF failed to be compatible, due to irreversible fouling of the RO membrane. The NF membrane, however, showed interesting results, due to membrane stability in terms of cleaning and fouling. The NF plant with 50% capacity gave a recovery of 75% and the RO plant gave a recovery of 60% versus the expected 92–95%. The long-term tests have indicated that the reminder of the membranes could be installed to achieve full capacity of the plant. This study also demonstrates the importance of selection of proper pre-treatment set-up for the RO system design.

The new generation of reagents for oil and gas production processes

The creation of environmentally and economically efficient products has been a major direction of scientific and practical developments in recent years [1 – 6]. Domestic and foreign experience shows that such products include reagents containing two and more ingredients which enter into physicochemical reactions and have the required operating characteristics in low concentrations [2 – 7].

Development of a high efficiency substitute natural gas production process

We have developed a high efficiency process for producing a substitute natural gas using LPG and naphtha as raw materials. In the process, sulfur poisoning of the steam reforming catalyst is protected and the amount of catalyst used can be reduced applying a high performance desulfurization technology developed. This technology enables the removal of trace amounts of sulfur which cannot be removed by a conventional hydro-desulfurization method. In addition, we have developed a high performance steam reforming catalyst which has a resistance to carbon deposition even under low S/C conditions. The catalyst makes it possible to reduce excessive steam for preventing carbon deposition, and to operate with high thermal efficiency.

Estimation of global biogeochemical controls and seasonality in soil methane consumption

Uptake by soils is a relatively small flux in the global budget of atmospheric methane, but CH4 consumption rates in soils could be susceptible to changes in land use and climate. Global estimates of the soil sink for atmospheric CH4 are usually made by multiplying averages of small chamber measurements for various ecosystem types (or other strata) by estimates of the area covered by each stratum. Process-level models driven by gridded databases can also be used to make global flux estimates, to evaluate potential effects of changes in climate and land use, and to identify weaknesses in both data and mechanistic understanding. Methane uptake by soils is an appropriate process to model globally because the probable controls are simple relative to many other microbially mediated soil processes of trace gas production and consumption. Field experience suggests that diffusion of atmospheric CH4 into the soil is the primary factor limiting rates of CH4 oxidation in many soils. We have applied a modified version of Fick's first law based on theoretical computations for diffusivity in aggregated media, together with a soil water balance model run on a 1δ global grid, to make independent estimates of CH4 uptake by soils worldwide. Uptake rates were assumed to be zero in very dry desert soils that are mostly devoid of microbial activity, in frozen soils, and in wetlands that are usually CH4 sources. Our mechanistically-based model supports a reference case for global net consumption of CH4 sources. Our mechanistically-based model supports a reference case for global net consumption of CH4 in soils of 17–23 Tg yr−1, which is near the middle of previously reported ranges, and is close to our own mean estimate from extrapolation of flux means across ecosystem strata (21 Tg CH4 yr−1). A new inference of our modeling approach is that over 40% of the soil sink for CH4 occurs in warm and relatively dry ecosystems, such as semi-arid steppe, tropical savanna, tropical seasonal forest, and chaparral. This model prediction results from a favorable climate regime, high porosity in coarse-to-medium textured soils, and low moisture content that permits rapid gaseous diffusion in these semi-arid and seasonally dry tropical ecosystems. Very few data on CH4 fluxes exist from these areas that can be used to compare with model predictions. Because of this paucity of data where uptake rates may be relatively high, and because humans have altered these landscapes extensively, our results suggest that more study is needed in seasonally dry ecosystems in order to understand the impacts of land-use change on soil sinks for methane.

Estimation of global biogeochemical controls and seasonality in soil methane consumption

Uptake by soils is a relatively small flux in the global budget of atmospheric methane, but CH 4 consumption rates in soils could be susceptible to changes in land use and climate. Global estimates of the soil sink for atmospheric CH 4 are usually made by multiplying averages of small chamber measurements for various ecosystem types (or other strata) by estimates of the area covered by each stratum. Process-level models driven by gridded databases can also be used to make global flux estimates, to evaluate potential effects of changes in climate and land use, and to identify weaknesses in both data and mechanistic understanding. Methane uptake by soils is an appropriate process to model globally because the probable controls are simple relative to many other microbially mediated soil processes of trace gas production and consumption. Field experience suggests that diffusion of atmospheric CH 4 into the soil is the primary factor limiting rates of CH 4 oxidation in many soils. We have applied a modified version of Fick's first law based on theoretical computations for diffusivity in aggregated media, together with a soil water balance model run on a 1δ global grid, to make independent estimates of CH 4 uptake by soils worldwide. Uptake rates were assumed to be zero in very dry desert soils that are mostly devoid of microbial activity, in frozen soils, and in wetlands that are usually CH 4 sources. Our mechanistically-based model supports a reference case for global net consumption of CH 4 sources. Our mechanistically-based model supports a reference case for global net consumption of CH 4 in soils of 17–23 Tg yr −1, which is near the middle of previously reported ranges, and is close to our own mean estimate from extrapolation of flux means across ecosystem strata (21 Tg CH 4 yr −1). A new inference of our modeling approach is that over 40% of the soil sink for CH 4 occurs in warm and relatively dry ecosystems, such as semi-arid steppe, tropical savanna, tropical seasonal forest, and chaparral. This model prediction results from a favorable climate regime, high porosity in coarse-to-medium textured soils, and low moisture content that permits rapid gaseous diffusion in these semi-arid and seasonally dry tropical ecosystems. Very few data on CH 4 fluxes exist from these areas that can be used to compare with model predictions. Because of this paucity of data where uptake rates may be relatively high, and because humans have altered these landscapes extensively, our results suggest that more study is needed in seasonally dry ecosystems in order to understand the impacts of land-use change on soil sinks for methane.

The regularities in the interaction of alkanes with CO 2 on oxide catalysts

Catalytic oxidation of C 1-C 7 alkanes by CO 2 as a non-traditional oxidant was studied on oxide catalysts. The supported manganese oxide catalysts are the most active, selective and stable. Methane is converted mainly into synthesis gas. Ethane and propane give products of oxidative dehydrogenation. In the case of C 4-C 7 alkanes at first direct dehydrogenation takes place and after that reverse water gas shift proceeds. Reactions of carbon dioxide with hydrocarbons were up to now still insufficiently studied. This is caused by small reactivity of both CO 2 and hydrocarbons. The recent interest in carbon dioxide reactions is two-fold: 1) the necessity to fight against the so-called green-house effect and 2) the exhaustion of raw carbon material sources [ 1 ]. The CO 2 molecule can be used a non-traditional oxidant. The best reducing agent for CO 2 is hydrogen. It was shown [2] that methanol synthesis proceeds not by direct CO + H 2 interaction, but by preliminary CO transformation into CO 2 CO+H 2O= CO 2+H 2 After that the interaction of CO 2 with H 2 gives methanol CO 2+3H 2= CO 3OH+H 2O But hydrogen is expensive. Hydrocarbons in the role of CO 2 reductants are more attractive. The most intensively studied reaction of hydrocarbons with CO 2 is methane conversion into synthesis gas CH 4+CO 2= 2H 2OH+2CO The main difficulty encountered when this reaction is used for the practical process of synthesis gas production is coking of the metal catalysts [3–6]. We have studied C 1-C 7 interaction with CO 2 over oxide catalysts [7–10] and it turned out that manganese oxides containing catalysts are effective both for methane transformation into synthesis gas and for C 2-C 7 alkanes dehydrogenation and oxidative cracking. What is especially important is that these catalysts are very stable during a long period without cake accumulation. This paper provides a review of our work in this field.

Dry Anaerobic Conversion of Municipal Solid Waste by Means of the Dranco Process

The Dranco process has been developed for the conversion of solid organic wastes, specifically the organic fraction of municipal solid waste (MSW), to energy and a humus-like final product, called Humotex. The Dranco process can be compared to landfill gas production, accelerated by a factor 1000. A Dranco installation with a digester of 808 m3 treating 10,500 tons of source separated waste per year will be constructed in 1991 at Brecht, Belgium. A description of the plant is elaborated. A demonstration plant of 56 m3 has been in operation for several years in Gent, Belgium using mixed garbage as a feedstock. The operating temperature in the digester is 55°C and the total solids concentration is ca. 32%. The mean gas production rate is 3.33 Nm3 CH4/m3reactor.day. The volumetric loading is 17.3 kg COD/m3reactor.day and the COD reduction is 55%. The gas production process is finalized in 3 weeks. The final product is dewatered and further stabilized in a 10 day aerobic post-treatment. The Humotex is free of pathogens. Low concentrations of heavy metals can only be obtained through separate collection of garbage. The Dranco process then also focusses on the digestion of source separated waste such as vegetable, fruit, garden and non-recyclable paper waste.

Experimental and Theoretical Investigation of Methane-Gas-Hydrate Dissociation in Porous Media

Summary Vast quantities of natural gas deposits exist in the form of solid hydrates. Methane gas hydrate was formed and dissociated for the first time in Berea core samples. A three-phase ID model was developed to simulate the process of gas production from Berea sandstone samples containing methane hydrate by means of a depressurization mechanism. The model closely matched the experimental data of gas and water production, the progress of the dissociation front, and the pressure and saturation profiles.

Area Waste-Management Plans for Drilling and Production Operations

Summary This paper details a process for identifying appropriate waste-managementstrategies in a specific area of operation. These strategies consider currentregulatory requirements, company policies, and economic and practical factors. Management practices covered include minimization, storage, handling, anddisposal. The strategies developed are communicated to field operations througha document specifically designed for effective use by field drilling andproduction personnel. The plan's objectives, development, content, and possiblealternative applications are presented, and examples from the development of anactual plan are given. presented, and examples from the development of anactual plan are given. Introduction One environmental issue receiving significant attention in recent yearswithin the oil and gas E and P industry is the handling and disposal of wastes. Heightened interest within the public and the regulatory agencies towardenvironmental issues has been an impetus for the industry to scrutinize itswastes and how they are managed. From a private company's perspective, properwaste management is an important part of business. A company must be concernedabout complying with applicable waste regulations, minimizing the impact of wastes on the environment, and reducing the disposed-of waste. All these mustbe done within certain economic boundaries. Also, eliminating or minimizingwaste generation is becoming more critical, both environmentally andeconomically, as a means of reducing waste-related liabilities and costs. Thispaper reviews the concept of the area waste-management plan as a means ofimproving the management of wastes generated by a company's drilling and production operations. The development and use of area waste-management plans allow a company to identify and communicate sound waste-management strategies effectively. The strategies are based on regulatory, environmental, technical, and economic criteria applicable to a specific geographic area of operation. Waste-Management Concerns A cursory review of Arco Oil and Gas Co.'s drilling and production operations identified several concerns regarding the handling and disposal ofcertain wastes generated by its operations. Production operations were viewed from a broad scope of operating facilities, including oil production (primaryand secondary), gas production, and gas processing. Drilling operationsobserved included drilling, workover, and completion. These field operationsoccurred in a variety of environmental and regulatory settings. Waste-management concerns generally focused on inconsistent minimization, handling, and disposal practices. Reviews of the operations and interviews withpersonnel revealed the specific reasons for these concerns. The primary reasonfor the concerns was an inadequate understanding of the wastes and themanagement options available. This misunderstanding was the result of severalfactors, including complex and changing regulations, unclear guidance on theenvironmental aspects of field operations, and the perception of competingenvironmental and economic goals. Regulatory Climate. Most state oil and gas agencies began regulating wastefrom drilling and production operations before the U.S. government started topass environmental statutes in the early 1970's. Historically, regulation of oilfield wastes has focused on drilling fluids and produced water. Since theearly 1970's, a number of federal and state environmental statutes andregulations have been passed that affect the management of oil and gas waste. Each state has developed regulations to control these wastes as specified inthe federal laws and as specified in the state's own environmental statutes. Though adequate, states' requirements for oil and gas waste management varysignificantly, reflecting the diverse geological and environmental conditionsin each state. Because of the historical emphasis on drilling fluid andproduced water, the regulations often are not specific on a waste-by-wastebasis. For operations on federal lands, companies must comply with separate.sometimes overlapping, regulations administered by different federal agencies(e.g., U.S. Bureau of Land Management and the U.S. Forest Service) in additionto the state's requirements. Also, the regulations have been amended frequentlyover the last 10 years. This complex regulatory climate, which changes withtime and geopolitical boundaries, contributes significantly to the lack ofunderstanding of requirements affecting waste management in the oil field. JPT p. 67

Comparison of galactomannan crosslinking with organotitanates and borates

Water-soluble polymers crosslinked with metal ions form stable gels that are used in oil and gas production processes. We present an investigation of the chemistry of the binding between guar galactomannans and both borates and titanates using NMR and dynamic light scattering. The two monosaccharides comprising guar — methyl-β-D-galactopyranoside and methyl-α-D-mannopyranoside — have been studied as model compounds. High resolution13C NMR detected complexation of the sugars with borate but displayed no sign of complexation with either of the two titanates even at high titanate concentrations. Dynamic light scattering studies demonstrated the existence of colloidal titanium dioxide particles for both titanate crosslinkers. The loss of free titanium to the colloidal particles reduces the concentration of titanium crosslinking sites to below the detectable limits of NMR. The role of colloidal titanium dioxide colloids in these crosslinking reactions has not been reported previously. Data are presented following the growth of these particles with time as a function of pH and salt concentration. The observed particle growth kinetics explains the observed sensitivity of the guar gelation process to these variables.

Economics of Natural Gas Resources and Supply: ABSTRACT

The relative availability and cost of finding and producing natural gas fields of varying size, located in regions of the United States at various depth intervals, are examined under different economic assumptions. First, historical trends related to the discovery and availability of natural gas are identified and discussed. These include trends in drilling activity, reserves production, and field-size distributions. Exploration, drilling, and production costs are presented and analyzed. This information is integrated, along with other data, as part of an economic evaluation of the natural gas discovery and production process in the United States. Finally, possible future discoveries of natural gas are projected based on varying assumptions related to the underlying distr bution of natural gas resources. End_of_Article - Last_Page 514------------

Energy needs versus environmental pollution: a reconciliation?

In this article I have presented, for discussion, a proposed system for energy generation by which the principal sources of environmental pollution by power plants could be eliminated. For stationary power plants the concept appears feasible technically and, according to my " horseback estimates," perhaps economically as well, depending upon the economic value of the by-products of sulfur, CO(2), water, and possibly nitrogen, and upon the price we are willing to pay for a clean environment .Thus, a more thorough engineering and economic analysis to explore these and other factors in greater depth seems warranted. In the case of turbine-driven vehicles, the technical and economic feasibility of widespread distribution and handling of the fuel constitutes a serious question, but one which deserves equally serious consideration before the possibility is discounted. The reports of the cited study panels notwithstanding, the technology required for the proposed system exists today, with one exception. This exception (which is not essential for trial of the system but will be required for its complete fruition) is the development of a nuclear reactor for the prime purpose of delivering process heat for the steam reforming of natural gas and, ultimately, for gas production from coal in a continuous process, such as those discussed by Pieroni et al. (16). Today's intermittent processes of coking and gas production are both archaic and themselves large sources of atmospheric pollution, and a development program aimed at advancing the technology of the coal industry in this regard would seem long overdue. The report of the PSAC Environmental Pollution Panel recommended "demonstration of the feasibility and economy of new developments for abating or controlling pollution through their use at Federal installations" and suggested the coalburning TVA power plants as a likely place for such demonstration. This suggestion is doubly appropriate since the TVA is in a region of subnormal " atmospheric ventilation" (8). By design these plants are adjacent to the AEC's Oak Ridge National Laboratory, and such a location would seem ideal for an experiment on the wedding of nuclear and fossil sources of energy. In comments on a preliminary draft of this article, proponents of "conventional " nuclear power pointed out that such power is hard to beat on the basis of cost, and that dissipation of heat to the air by way of cooling towers can also be accomplished in conventional plants (17). These observations are individually correct but not compatible: the low power costs cited are for very large plants [of the order of 1000 mega-watts lectrical) and larger], and the costs of cooling towers and associated equipment needed to dissipate such large amounts of heat [of the order of 2000 megawatts (thermal)] to air from a closed cycle would offset the power cost advantage of the large plant. In regard to the proposed use of nuclear process heat, Weinberg (20) has expressed doubt that much advantage can be derived from this approach because the temperatures involved are too high for low-cost reactors, and heat transfer from surfaces could involve materials problems. In the case of gas production, this is indeed an anticipated problem-not a technologically insuperable one, but a problem of reducing the cost of the materials required (16). Indeed, Weinberg himself has mentioned this possible use of nuclear heat in a recent publication discussing the steam reforming of coal to liquid fuel(21). Also, an improved process for synthesizing methane from lignitec has recently been reported (22). Since the earlier studies date back a decade, a new look at the problems and costs involved relative to the benefits to be derived (not the least of which could be new vigor for the coal industry) would seem to be in order. In the case of steam reforming of natural gas, the temperature level (about 1500 degrees F) is such that the technology is available today, and a process-heat-reactor design study could be initiated without awaiting further developments.

The Prediction of Flow Patterns, Liquid Holdup and Pressure Losses Occurring During Continuous Two-Phase Flow In Horizontal Pipelines

Abstract This paper presents the results of an investigation of two-phase, gas-liquid flow in horizontal pipelines. Experimental data were taken in three field-size, horizontal pipelines, two of which were constructed for this purpose. The data were obtained using water, distillate and crude oil separately as the liquid phase, and natural gas as the second phase. Experimental pressure-length traverse, liquid holdup and flow-pattern data were collected for each set of flow rates. These data were used to develop three correlations that are presented herein. The liquid-holdup values correlated with various flow parameters without regard to the existing flow pattern. The same was true for the energy-loss factors. A new flow-pattern map is presented that appears to be quite reliable, but not required for the pressure-loss calculations. The liquid-holdup correlation and the energy-loss factor correlation are used in conjunction with a two-phase flow power balance, developed during this study, to predict the pressure losses that occur during gas-liquid flow in horizontal pipelines. A recommended calculational procedure is given, as well as a statistical analysis of the results. This procedure lends itself to computer application, since several small pressure decrements are needed to calculate a pressure-length traverse. The correlations are shown graphically, but may be curve fitted with existing curve-fitting computer programs. Introduction Due to the frequent occurrence of gas-liquid flow in pipelines and the desire to accurately calculate the pressure losses that occur in these lines, two-phase flow is of considerable interest to the petroleum, chemical and nuclear industries. In the petroleum industry, gas-liquid mixtures have been transported over relatively long distances in a common line due to the advent of centralized gathering and separation systems. Long two-phase flowlines are usually accompanied by large pressure drops which influence the design of the system. Gas-lift installations are designed on the basis of known tubing pressures at the wellheads. The horizontal flowline connecting the wellhead and the separator system must be correctly sized in order to minimize the horizontal flowline pressure losses and the wellhead tubing pressure. Practically all oilwell production design involves horizontal two-phase flow in pipelines. All of the flow processes of oil and gas production must be studied simultaneously to insure good well design. Since the beginning of offshore oilfield development, long horizontal flowlines have been constructed. Because pressure losses greatly influence the performance of producing wells, a method is desired that can be used to predict such pressure losses and select optimum flowline size. Several types of gas-liquid flow exist, and many of these are discussed by Gouse. The study of pressure gradients, fluid distributions and flow patterns that occur in horizontal multiphase flow is made difficult by the great number of variables involved. The various flow regimes give rise to changing velocities of the fluid particles in all directions. These instabilities of the interface between the gas and liquid prohibit the determination of actual vector velocities of fluid particles in each phase. Also, it is practically impossible to arrive at correct sets of boundary conditions. Therefore, most investigators have concluded that a solution to the problem by the classical fluid dynamics approach, whereby the Navier-Stokes equations are formulated and solved, is far too complex. Other methods must be utilized to develop general correlations that will predict the behavior of gas-liquid horizontal flow systems. Multiphase flow studies have sought to develop a technique with which the pressure drop can be calculated. Pressure losses in two-phase, gas-liquid flow are quite different from those encountered in single-phase flow; in most cases an interface exists and the gas slips past the liquid. The interface may be smooth or have varying degrees of roughness, depending on the flow pattern. Therefore, a transfer of energy from the gaseous phase to the liquid phase may take place while energy is lost from the system through the wetting phase at the pipe wall. Such an energy transfer may be either in the form of heat exchange or of acceleration. Since each phase must flow through a smaller area than if it flowed alone, amazingly high pressure losses occur when compared to single-phase flow. Most investigators of horizontal two-phase flow phenomena have chosen to separate their experimental data into several groups of observed flow patterns or regimes.

Comparisons between gas and electricity on the basis of coal economy

For some time it has been common practice to compare the application of gas and electricity on the basis of production efficiency and coal-economy efficiency. Figures stated by independent authorities and in recent report suggest that electric heating involves 60% to over 100% higher coal consumption than gas heating. The paper shows that such inferences are erroneous; that in the case of joint products?such as gas and coke?the promiscuous use of percentage efficiencies can be misleading; that a reliable method of comparison consists in estimaging the quantities of solid fuel, gas and electricity required to supply a given schedule of domestic heating by various combinations of means, and calculating the comparative total amounts of raw coal necessary. Applied to the principal combination of appliances put forward in the Egerton Report and to a combination chosen by the author, the method proves that, with present processes of electricity and gas production and utilization, no decided difference in regard to coal economy exists between gas and electricity for domestic heating purposes, and that this factor can therefore be eliminated from comparisons between the two rival commodities.