一個多世紀以來，煤和其他燃料中的能源一直被用來產(chǎn)生蒸汽發(fā)電。今天，由于全球人口不斷增長，城市化和工業(yè)化程度不斷提高，以及消除能源貧困的努力，快速發(fā)展國家的能源需求主要由煤炭推動。根據(jù)英國石油公司（BP）對2014年世界能源的統(tǒng)計報告，2000年至2013年間，煤炭在全球能源消費中所占份額攀升至30.1%，為1970年以來的最高水平。中國古代哲人常說，講到物質(zhì)，就講到得失，而在人的事務(wù)中，有利有弊，能源的生產(chǎn)和利用是人的根本事務(wù)。不可否認，煤炭支持了工業(yè)化、現(xiàn)代文明的發(fā)展，但也存在著挑戰(zhàn)，如二氧化碳等排放。許多清潔煤技術(shù)都是商用的，高效、低排放（HELE）燃煤電廠必須在向更清潔、低碳能源的未來過渡中發(fā)揮重要作用。用超超臨界電站取代或改造低效亞臨界電站，可使單位電力碳排放量減少約20%或以上。雖然要實現(xiàn)國際減緩氣候變化的目標，可能需要進一步削減，但全球HELE技術(shù)的部署是一個可以立即產(chǎn)生重大影響的步驟。根據(jù)國際能源機構(gòu)，只有約29%的現(xiàn)有燃煤發(fā)電機組可以進行碳捕獲、利用和儲存改造。因此，提高效率是實現(xiàn)重大減排的第一步。中國正通過積極提高其煤炭發(fā)電機組的效率來進行必要的投資。該國已經(jīng)看到了相當(dāng)大的改善，用使用HELE技術(shù)的大型電廠取代了舊的、效率低下的和較小的電廠。例如，上海外高橋3號超超臨界燃煤電廠的標準排放量不到中國天然氣發(fā)電廠限值的一半。還有一些非傳統(tǒng)的提高能源利用效率的方法正在構(gòu)想和部署之中。例如，以煤炭為基礎(chǔ)的電、熱、燃料多聯(lián)產(chǎn)可以解決中國交通和工業(yè)部門的排放問題，從而實現(xiàn)全面的能源轉(zhuǎn)型。此外，世界上第一臺600兆瓦超臨界循環(huán)流化床的示范，為低階煤、廢棄物和生物質(zhì)的高效利用奠定了基礎(chǔ)。在南非，一家獨立的電力生產(chǎn)商正尋求利用煤炭地下氣化提供急需的基本負荷電力。這一問題的基石是集中在許多方法，煤炭可以用來填補全球能源需求的最高效率和最低的排放量可能。因此，我們希望本期的內(nèi)容能夠引發(fā)對HELE技術(shù)這一重要課題的深入探討。我代表編輯組，希望你們喜歡。

For well over a century the energy in coal and other fuels has been used to  create steam for electricity generation. Today, due to a continuously expanding global population, increasing urbanization and industrialization, and energy  poverty eradication efforts, energy demand is growing—fueled primarily by coal in  rapidly developing countries. According to BP’s Statistical Review of World Energy  2014, coal’s share of global energy consumption climbed between 2000 and 2013,  to 30.1%, the highest amount since 1970. Ancient Chinese philosophers often said that when speaking of material things, one  speaks of gains and losses, while in human affairs there are pros and cons—energy production and utilization is a fundamental human affair. There is no denying  that coal has supported the development of an industrialized, modern civilization,  but there are also challenges, such as CO2 and other emissions. Numerous clean  coal technologies are commercially available and high-efficiency, low-emissions (HELE) coal-fired power plants must play an important role in the transition to a  cleaner, lower-carbon energy future. Replacing or retrofitting a low-efficiency subcritical plant with an ultra-supercritical  plant could reduce carbon emissions per unit of electricity by about 20% or more.  While deeper reductions may be necessary to meet international climate mitigation goals, global HELE technology deployment represents a step that can have an  immediate, substantial impact. According to the International Energy Agency, only  about 29% of the existing coal-fired power fleet can be retrofitted for carbon capture, utilization, and storage. Thus, efficiency improvements are the first step on the  road to major emissions reductions.  China is making the needed investment by actively increasing the efficiency of its  coal-based power fleet. The country has already witnessed considerable improvements by replacing older, inefficient, and smaller power plants with large ones using  HELE technologies. For instance, criteria emissions from the Shanghai Waigaoqiao  No. 3 ultra-supercritical coal-fired power plant are less than half of China’s limits for  natural gas power plants.  There are also unconventional approaches to improving the efficiency of energy  utilization that are now being conceptualized and deployed. For example, coalbased polygeneration of electricity, heat, and fuel could address emissions from the  transportation and industrial sectors in China—leading to a comprehensive energy  transformation. In addition, the demonstration of the world’s first 600-MWe supercritical circulating fluidized bed has set the stage for the HELE utilization of low-rank  coals, wastes, and biomass. In South Africa one independent power producer is  looking to HELE underground coal gasification to provide much needed baseload  electricity.  This issue of Cornerstone is focused on the many ways that coal can be used to  fill global energy demand with the highest efficiency and lowest emissions possible. Thus, our hope is the content in this issue will spark deep engagement on the  important topic of HELE technologies. On behalf of the editorial team, I hope you  enjoy it.