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The current status of liquefied gas supply and discussions on expanding its use: Urban gas use in China has a history of 130 years, particularly over the past two decades； Cities are accelerating the construction of gas pipelines; gas has become an essential infrastructure and a symbol of modernization in cities. It is reported that there are over 300 cities equipped with gas facilities, accounting for more than 60% of the total number of cities in the country. The types of gas include natural gas, city gas, liquefied gas, mine gas, and amateur gas; among these, more than 150 cities use liquefied gas, and the consumption of gas as well as the number of people who use it account for a significant proportion. This article discusses the current status of LPG supply and the expansion of its applications. 1. The role of liquefied gas in the composition of urban gas 1.1 Overview In the 1980s, with the rapid development of the petroleum industry in China, liquefied gas was widely used in cities, and its consumption continued to increase. Currently, the annual consumption of liquefied gas exceeds 3 million tons, which is four times the amount at the end of the Seventh Five-Year Plan period. In addition to being supplied by domestic refineries, an increasing amount of liquefied gas is imported, resulting in a market situation characterized by multiple sources of supply for this fuel. More than twenty new liquefied gas terminals and distribution bases have been built in coastal cities of our country such as Guangdong, Fujian, Hainan, Shanghai, Zhejiang, and Jiangsu. The uses of liquefied gas are also expanding, and the level of technical equipment has approached that of developed countries. However, in the development of liquefied gas in our country, there are issues such as fragmented operations, small scale, low equipment utilization rates, improper use, and poor economic efficiency; these problems require comprehensive research by relevant parties to be resolved. 1.2 The proportion of liquefied gas in the composition of urban gas: Internationally, in large cities, gas accounts for more than 25% of the total energy and fuel supply; for example, in the United States it’s %, in the CIS it’s 29%, and in Canada it’s 27%. Natural gas – or imported liquefied natural gas – is preferred as the main source of gas, with liquefied gas serving as a supplementary source, as is the case in Paris and New York ； Tokyo and others ； In contrast, medium and small cities, as well as those without access to natural gas supply, rely mainly on purchased liquefied gas as their energy source, such as cities in Singapore, Thailand, Japan, and elsewhere. Analyzing the current situation of urban gas in China, in megacities such as Beijing and Tianjin, liquefied gas was originally the main source of gas, but now efforts are being made to develop natural gas and artificial gas ； Shanghai relies primarily on Renwang gas as its main fuel source, with liquefied gas serving as a supplementary source; introducing natural gas is planned during the Ninth Five-Year Plan period. Some large and medium-sized cities develop both city gas or natural gas alongside liquefied gas, but a considerable number of cities use liquefied gas as their sole gas source. In line with the development strategy for urban gas in our country, coal gas, natural gas, liquefied gas, mine gas, and other types of gas will continue to be used for a considerable period of time. The selection of energy sources for a city should follow the principle of \"adjusting to local conditions and using them reasonably\". Together, large and mega agricultural cities should achieve gasification as soon as possible. The approach to this is to give priority to the conditional introduction of natural gas; where such conditions do not exist, artificial gas should be developed as the main option. In areas outside the city and within it that are not connected by gas pipelines, liquefied gas can be used ； For medium-sized cities that do not have access to external gas supplies or the means to build their own gas plants, liquefied gas can be given priority as an option ； In small cities and towns, liquefied gas should be given priority where conditions permit. Urban-owned gas plants should take into comprehensive consideration technical and economic factors such as raw material sources, gas production methods, distribution systems, target users, and their proportions, operate in a manner that matches available resources, and develop at an appropriate pace in order to minimize financial losses. For cities with liquefied gas resources, including those equipped with liquefied gas import terminals and facilities, it is advisable to consider supplying gas to cities within the province or nearby areas in order to expand business scale and improve economic efficiency. In summary, liquefied gas accounts for a certain proportion in the composition of urban gas, and this proportion is related to the scale of the main gas supply source; it should be taken into consideration comprehensively when implementing urban gasification. 2. Scope of application of liquefied gas in urban gas: With an abundant supply of liquefied gas resources, its scope of use in urban gas is also expanding. It is no longer limited to supply to users through individual gas cylinders alone; it has now been extended to areas such as artificial gas and natural gas. Based on applications both domestically and internationally, the following can be listed: 2.1 Direct supply: Liquefied gas is supplied directly to users via gas cylinders, storage tanks, or regional vaporization units, for use in households, commercial establishments, industries, power generation, heat pumps, vehicles, and so on. 2.2 Blended supply: Liquefied gas is vaporized and blended with air to supply mixed gases of different compositions. Used as a substitute for natural gas, for transition purposes, for peak shaving, or as an emergency gas source in case of accidents ； Substitute for artificial gas, flexible gas source for peak shaving ； In cold areas with poor quality liquefied gas, supply is provided to users through a pipeline network. 2.3 Artificial gas source (or production of alternative natural gas): Liquefied gas is used as a raw material for producing artificial city gas or as a heat source; it is generally mixed in certain proportions with gases having a lower calorific value in order to meet the calorific value standards for city gas. It is also used to produce substitute natural gas for hydrocarbon conversion furnaces. 2.4 Application status: In China, liquefied gas is mainly used for the first category, while categories two and three have only begun to be developed and utilized in the past decade. Abroad, it is already widely used in this area. Such as Japan’s total liquefied gas consumption in 1993 ； 20 million tons, accounting for 5% of total energy consumption; of this amount, 15.65 million tons are imported and 4.65 million tons are produced domestically, with an annual increase of over 2%. In terms of usage: household use accounts for 6.7 million tons, urban gas supplies account for 2.85 million tons, and automobiles account for 1.85 million tons. The penetration rate of domestic gas in Japan is 98%, with over 60% of users relying on liquefied gas, amounting to 22.75 million households. China’s liquefied gas market has matured, but its application in certain industries has yet to begin, such as the use of liquefied gas as fuel for vehicles, liquefied gas-based air conditioners and heat pumps, as well as the development and use of liquefied gas in industry and power plants. 3. Discussions on expanding applications 3.1 Changing from single-bottle supply to multiple supply methods. Although bottled liquefied gas offers advantages such as flexibility and rapid development, it also presents numerous safety issues; as a result, efforts are being made to promote various supply methods such as group gasification, community gasification, and blending. The applicable scenarios are as follows: 3.1.1 Gasification: The liquefied gas supplied in gas cylinders vaporizes due to the absorption of heat from the surrounding environment by its own moisture and heat; if forced vaporization is required, hot water, steam, or electricity is used as a heat source. For medium and small-scale systems (with a liquefied gas capacity of 4 tons per hour or less), hot water is generally used as the heat source ； For large-scale systems (with a liquefied gas capacity of 4 tons per hour or more), low-pressure steam is generally used as the heat source ； Single-family homes include gas supply for small users (200 kilograms per hour of liquefied gas), and electricity can also be used as a heat source. 3.1.2 Blending: The mixing of gaseous liquefied gas with air or gas with a low calorific value is generally achieved using entrainment, mixing valves, or mixers with equal mixing ratios. Among them: for mixed gases of medium and low pressure as well as medium and small scale, an ejector type (Venturi) is generally used; the gas flow rate can be adjusted from 0-100%, while the nozzle setting ranges from 20-100%. The allowable range for pressure is 0.25 Mpa, and the ejector ratio remains fixed. Mixing valves and mixing ratio valves are generally used for high and medium pressure applications, as well as for large and medium-scale gas mixing processes. The gas flow rate can be adjusted, and the mixing ratio ranges from 0 to 100%. The mixing pressure is determined by the pressure of the air compressor (or blower) used, as well as that of the low-calorific-value gas; typically, the mixing pressure lies between 0.07 and 1.05 Mpa. 3.1.3 Supply pressure: The supply pressure for gasification or blending should be determined in accordance with the pressure standards for gas distribution (see table below). Generally, a two-stage or three-stage system is adopted for transmission and distribution pressure. That is, a pipeline network system with a two-stage configuration of medium pressure – low pressure or high pressure (B) – low pressure ； A pipeline system with a three-tier classification of high pressure (B), medium pressure, and low pressure. For medium and small-scale applications in cold regions where the C3 content in the liquefied gas is low, medium-low or high (B)–low pressure levels for distribution should be used to prevent the re-liquefaction of gaseous liquefied gas. For use in natural gas and synthetic gas, it should generally be considered based on the distribution pressure of the main gas source. 3.1.4 When liquefied gas mixtures are used for natural gas or artificial gas, due consideration should be given to the mixing ratio of the mixture as well as its mixing proportion with the gas from the respective main source. At the same time, due to the certain differences in the combustion characteristics of natural gas, city gas, and liquefied gas, there should be good interchangeability between the mixed gas and the gas from the main supply source. Their indices such as the Whiteness Index (W), Combustion Potential (Cp), flame out, backfire, yellow flame, and carbon deposition must be compatible so that the cooking appliance can function properly. 3.2 Use as vehicle fuel: As early as the 1970s, countries such as those in Northern Europe and Japan began researching and testing propane and butane gases as alternatives to gasoline and diesel for use in vehicles, with practical application starting in the 1980s. Compared to gasoline and diesel, it can reduce air pollution, especially the pollution at a height of 1 meter above the ground. Propane and butane contain no lead or sulfur; as a result, their combustion exhaust does not contain lead or sulfur oxides. The CO content is reduced by 75% (LPG has a CO level of less than 0.5%, while gasoline typically has 3% CO). The aromatic hydrocarbon content is reduced by 80%, and black smoke emissions are decreased by 50%. Nitrogen oxide levels remain roughly the same, though they decrease at low speeds or during deceleration. It can also improve vehicle performance: the high octane rating of LPG allows for the use of a higher compression ratio, which enhances engine efficiency, extends its lifespan, and reduces lubricant consumption by 50%. The volume consumption per 100 kilometers for vehicle LPG is roughly the same as that for gasoline and diesel, with a slight reduction of 5%; due to the difference in density, it can be reduced by 15% on a weight basis. For use in vehicles, LPG in Europe is a mixture of propane and butane in a ratio of 25:75 or 75:25, with strict control to keep the olefin content at no more than 10%. In Japan, LPG for vehicles is generally made from butane and propane. The disadvantages of using LPG in vehicles are that the storage tanks take up a significant amount of space in the vehicle’s trunk, which increases the vehicle’s weight and cost; in addition, strict safety measures are required. In Western Europe, Japan, Southeast Asia, etc., for vehicle-use LPG, efforts are first made in small vehicles such as cars, while in Western Europe it is more commonly used in commercial vehicles. Engine modifications include those that use only LPG, as well as those that use both fuels. In Japan, all rental vehicles use LPG; France allowed dual-fuel vehicles since 1984, while the Netherlands, Italy, Australia, and Thailand make more use of them in small vehicles. Argentina, Canada, France, Italy in the 1980s ； Countries such as New Zealand, Spain, the United Kingdom, the United States, and Austria are converting urban diesel buses to use LPG fuel, or equipping them with diesel-LPG dual-fuel engines, in order to adapt to the frequent changes in driving conditions of urban buses and to overcome the poor performance of diesel engines at low speeds. In the late 1970s, China carried out systematic research and development in this area. In the 1980s, Japan donated five used E-N430 LPG cars to Shanghai; these cars used LPG produced by the Jinshan Petrochemical Complex in Shanghai as fuel, and they performed well. They consumed 14 liters of LPG per 100 kilometers (equivalent to 7.84 kg), compared to 12.5 liters of gasoline (equivalent to 9 kg). With a tank capacity of 103 liters, each fill allowed the cars to travel 520 kilometers. The average driving range in urban areas was 150 kilometers. These vehicles operated under the same conditions as gasoline cars, and they had the advantages of easy starting when cold, rapid acceleration, lower fuel consumption, and reduced emissions. Recently, Taiwan has also been accelerating the development of LPG cars, with two new gas filling stations having been built in Taichung. Using LPG in vehicles is a mature technology; in China, efforts to promote its use still need to address issues such as the economies of scale in engine modifications, the location and construction of urban LPG filling stations, the quality standards for vehicle LPG, as well as relevant fire safety measures. 3.3 LPG heat pumps: Gas heat pumps come in two types – compressive (gas-driven) and absorption type – and are generally used in large buildings and regional heating/cooling systems for heating, cooling, and hot water supply. This method of cooling and heating can be moderated. It addresses the imbalance between gas demand in winter and summer as well as the constraints on electricity supply, while reducing environmental pollution. Based on research and usage patterns in countries such as the United States, France, Germany, and Japan, LPG-powered engines can operate for 50,000 to 60,000 hours, whereas diesel and gasoline engines have a lifespan of around 10,000 to 20,000 hours. In France, such systems were used for home heating; the heat output of these systems was 16 kilowatts, powered by a 4-kilowatt LPG (or other gas) piston compressor ； Absorption heat pumps are widely used; the common refrigerant absorbers used in them are lithium bromide, water, and ammonia. Although absorption heat pumps have disadvantages such as a lower fuel utilization coefficient compared to compression heat pumps and higher relative heat losses, their daily maintenance costs are low. Japan has produced household LPG air conditioners, and their selling prices and costs are currently **higher than those of electric air conditioners. The initial investment and operating costs of centralized gas air conditioners can be comparable to those of boilers and electric air conditioners, and there are several manufacturers in China producing directly-fired lithium bromide absorption air conditioners. In addition, countries such as Ireland, Italy, and France **use LPG-based small-scale cogeneration in residential buildings, as well as in systems combined with electric compression heat pumps. It can save 35% on primary energy consumption, and is more appropriate for use on a regional scale in areas where there is a power shortage or where electricity prices are higher than those of gas. The development of gas heat pump technology and equipment in our country is still in its initial stages. New technologies related to gas heat pumps have already been recognized and valued by those in the gas industry, and it is expected that in the near future, a range of products based on such gas heat pump technologies will be put into use in our country. 3.4 Small steam boilers: Boilers that use oil or coal as fuel remain one of the sources of pollution in cities. With the development of the urban tertiary industry, hotels, inns, large commercial facilities, and office buildings all require steam and hot water. The use of high-efficiency small gas boilers or hot water heaters not only helps to save energy but also **improves the urban environmental conditions. It is reported that the heat efficiency of small gas boilers is generally between 85-88%, while the recovery rate of waste heat can exceed 95%. Moreover, these boilers are compact and require less space; however, safety requirements must be met regarding the storage and supply of LPG. 3.5 Gas turbines: In developed countries, in addition to natural gas, gas turbines also use LPG as fuel. When used in power plants, they offer advantages such as simpler operation processes compared to coal and oil-fired turbines; high flexibility in scheduling; fast start-up and shutdown times; reduced pollution from waste gases; lower energy consumption; and lower initial investment and electricity production costs. Their combustion efficiency reaches 46-47%, which is 10% higher than that of conventional power plants. Gas turbines are also used in industry to generate power and heat energy; combined heat and power generation is employed when electricity prices in the grid are high. In recent years, China’s power systems have been actively developing and promoting gas-based power generation technology; once LPG is adopted, its consumption will increase significantly. 4. Conclusion: Although the development and application of liquefied gas in our country have a history of just over thirty years, its growth rate has been rapid. Indeed, it is expected that demand for LPG will more than double during the Ninth Five-Year Plan period. A number of new storage and transportation facilities with a capacity of over 100,000 cubic meters are being built in China. Interest in expanding the use of LPG is growing rapidly, and practical efforts are underway; it holds great potential for application across various industries. The level of its application technology will also tend to improve and advance, reaching the level of developed countries.