2023/07/04 生質能與碳捕集和封存：英國實現淨零排放所依賴的技術

生質能與碳捕集和封存：英國實現淨零排放所依賴的技術
BECCS: the carbon capture technology the UK is relying on to reach net zero發表日期：2022-5-17
作者：Raffaella Ocone；翻譯：柯端榕；校稿：林詩軒
引用來源：https://theconversation.com/beccs-the-carbon-capture-technology-the-uk-is-relying-on-to-reach-net-zero-182176
 
『參考要點』：英國政府仰賴生質能源碳捕集技術（BECCS）來實現淨零排放目標。然而，BECCS的效果和可行性仍存在著許多不確定性。燃燒木材可能產生更多的二氧化碳排放量，且生質能源需要大片土地，這對野生動植物造成威脅。應該全面評估BECCS所涉及的各種因素，並持續推動其他永續能源和碳捕集技術的研發。
『相關字彙』：BECCS (Bioenergy with Carbon Capture and Storage)（生質能與碳捕集和封存）、Net zero emissions（淨零排放）、Carbon dioxide（二氧化碳）、Carbon emissions（碳排放）、Bioenergy（生質能源）
 
英國政府依賴生質能源發電廠正在試驗的碳捕集技術，以達成其氣候變遷目標。2022年5月，英國最大的可再生能源發電廠（Drax）宣布計畫在其位於北約克郡的發電廠進行一項新的捕集技術的開創性試驗。
The UK government is counting on the carbon capture technologies that bioenergy power plants are trialling to meet its climate change goals. Last week the UK’s largest renewable energy power plant, Drax, announced plans for pioneering trials of a new capture technology at its North Yorkshire power station.
整體而言，英國每年花費數億英鎊在這些木材燃燒發電廠上，而這項技術據稱可以消除這些排放物，但它是否能夠實現英國和全球所需的碳排放減少呢？要回答這個問題，首先重要的是要了解科學家所說的「負排放」一詞含義，尤其是如果您希望自己能解讀氣候變遷的新聞。
Overall, the UK spends hundreds of millions of pounds every year on the wood-burning power stations this technology would supposedly remove the emissions of. But can it deliver the kind of reduction in carbon output the country and the world needs? To answer this question, first it’s important to understand what scientists mean by the term “negative emissions” – especially if you want to decipher climate change news for yourself.
想像一下，垃圾清潔工罷工了一個月，期間垃圾大量積累。清潔工返回工作後，在有限的工作時間內無法清理掉積累的垃圾，所以市政府雇用了額外的工人。因此，在罷工後的一段時間內，產生的家庭垃圾量少於收集的垃圾總量。垃圾的淨生產量是負數的，即使有一段時間街道上仍有垃圾。
Imagine that household waste collectors go on strike for a month, during which huge amounts of rubbish accumulate. Upon returning to work, the collectors working their usual shifts aren’t able to clear the backlog, so the council hires extra workers. For a period after the strike, the amount of household waste produced is therefore less than the total rubbish being collected. The net production of waste is negative – even if, for a period, there is still rubbish in the streets.
從上述例子中，垃圾代表的是溫室氣體排放，以及負排放制度有可能發生的情況。然而，在過去的幾十年裡，全球溫室氣體的產量仍然很高，而被清除的非常少。目前補充大自然去除碳的嘗試很大程度上都未能成功。例如，美國政府投資數十億美元用於捕集燃煤發電廠釋放的碳，但大部分碳捕集設施從未建置，主要是因為該技術過於昂貴。
The rubbish in this example represents greenhouse gas (GHG) emissions, and what a regime of negative emissions could look like. In the last few decades, however, the worldwide levels of GHG produced remained high and very little was removed. Attempts to supplement nature’s processes for removing carbon have largely proved unsuccessful. For example, the US government invested billions of dollars in technology to capture carbon released from coal power plants, but most of these carbon capture units were never built – largely because the technology was so expensive.
大多數情況下，我們仍然依賴於天然棲息地，如森林、紅樹林和沼澤地，來將碳從大氣中移除。但是，隨著海平面上升，英國的鹽沼地可能會消失，世界上大片的紅樹林已經被清除並用於養殖蝦類，而我們正在以驚人的速度失去森林，其中原因包括森林砍伐和野火。
Mostly, we still rely on natural habitats such as woodlands, mangroves and peatland to remove carbon from the atmosphere. But UK salt marshes could disappear under rising sea levels, huge swathes of the world’s mangrove forests have been cleared for shrimp farms, and we are losing forests to timber logging and wildfires at an alarming rate.
如果我們採取所有可能的技術來移除溫室氣體排放，使我們的排放量低於產生量（就像我們雇用了更多的清潔工），我們將進入一個負排放制度。這是否行得通呢？
If we put in place all the potential technologies for removing GHG emissions so that we remove more than we produce (we hire more rubbish collection workers), we would instead be in a regime of negative emissions. So how feasible is this?
什麼是BECCS？
What is BECCS?
生物質或生質能源是英國繼風能之後的第二大可再生能源來源。生質能源是透過燃燒物質，主要是木屑顆粒來產生的。生質能與碳捕集和封存（BECCS）主要目的為捕集燃燒木屑顆粒和作物釋放的碳，並將碳封存到地下。這項技術被認為是負碳排放的，因為它有效地從大氣中去除碳。英國最大的可再生能源發電廠（Drax）的一個BECCS試點計畫在2019年成功捕集了碳，該發電廠計畫在2027年完全實現碳捕集技術的運營。
Biomass or bioenergy is the UK’s second-largest source of renewable energy after wind power. Bioenergy is generated by burning matter, mostly wood pellets. Bioenergy with carbon capture and storage (BECCS) aims to capture the carbon released from burning wood pellets and crops, and store the carbon deep below the ground. This technology is considered carbon negative because it effectively removes carbon from the atmosphere. A BECCS pilot project at Drax captured carbon in 2019, and the power station aims to have carbon capture technology fully operational in 2027.
到目前為止，BECCS的支持者表示它將在因應氣候變遷方面起到關鍵作用。然而，現實情況往往並不如表面看起來的那麼簡單。首先，BECCS只計算燃燒木材釋放的碳。事實上，碳在整個過程中產生，種植樹木、收割、將木材轉換成顆粒、運輸顆粒等。保守估計，製造木屑顆粒和運輸它們的碳排放占這一過程中排放總量的大約四分之一，而碳捕集和封存本身就是一個高度耗能的過程。
So far so good. BECCS advocates say it will be key in the fight against climate change. However, life is never easy as it first looks. For a start, BECCS only accounts for carbon released when the wood is burned. In reality, carbon is generated throughout the process chain: planting trees, harvesting them, turning the wood into pellets, shipping the pellets. Conservative estimates show making wood pellets and shipping them accounts for about a quarter of the carbon released in this process. And carbon capture and storage is itself a highly energy-intensive process.
回到我們先前的例子，忽視這些碳排放就像市政府沒有考慮到清潔工需要維護垃圾車和分類不同回收物所需的時間一樣荒謬。此外，燃燒木材產生的二氧化碳（CO₂）排放量可能比化石燃料還要多。準確計算燃燒木材排放的二氧化碳並不容易，因為存在著眾多變數，而且這些計算往往假設一個穩定的過程，一個正確的分析應該考慮到取代和管理已經被砍伐的森林所需的時間。
To return to our earlier example, overlooking these carbon emissions would be like the council failing to factor in the time workers need to maintain rubbish collection trucks and separate different recycling materials. What’s more, burning wood can produce more CO₂ emissions than fossil fuels. Providing a precise account of the emissions from burning wood is not an easy task as there are so many variables. And calculations tend to assume a steady process. A correct analysis should factor in things like rotation time to replace and manage the harvested forest.
鑒於燃燒木材所產生的熱量遠遠少於燃燒石油或煤炭，生質能源的木材實際上可能會產生更多的凈二氧化碳，而英國政府正依賴BECCS來實現其淨零排放策略。
Given that burning a unit of wood generates considerably less heat compared with burning a unit of oil or coal, wood for bioenergy can actually produce more net CO₂. Yet the government is relying on BECCS for its net zero strategy.
這項技術到底多有用呢？
So how useful is this technology?
英國是世界上最大的生質能源進口國，2020年進口超過900萬噸的木屑顆粒，燃燒約700萬噸的木屑顆粒相當於燃燒2,500萬棵樹。2020年，英國政府承諾投入130億英鎊（約新台幣5,137億）支持木材燃煤發電廠，其中包括100億英鎊（約新台幣3,950億）用於Drax發電廠。能源智庫Ember估計，生物質發電廠每年獲得3.33億英鎊（約新台幣131億）的碳稅減免，此外還有直接的補貼。
The UK is the largest importer of bioenergy in the world, bringing in more than 9 million tonnes of wood pellets in 2020. Burning around 7 million tonnes of wood pellets is equivalent to burning 25 million trees. In 2020, the UK government pledged to spend £13 billion to support wood-burning power stations, including £10 billion at the Drax power station. Energy thinktank Ember estimates that biomass generators are getting carbon tax breaks of £333 million a year in addition to the direct subsidy.
然而，最新的聯合國政府間氣候變遷專門委員會報告對BECCS的評價不高。報告指出：「生質能源的使用可能導致排放增加或減少，這取決於部署規模、轉換技術、被替代的燃料以及生物質的生產方式和地點。」總的來說，該報告對BECCS的實用性還存在著很多未知。
Yet the latest UN Intergovernmental Panel for Climate Change  report is lukewarm about BECCS. It states: “The use of bioenergy can lead to either increased or reduced emissions, depending on the scale of deployment, conversion technology, fuel displaced, and how and where the biomass is produced.” Overall, the report leaves us in the dark about how useful BECCS can be.
問題的規模
The scale of the issue
利用植物光合作用去除二氧化碳是世界上最好的碳捕集技術。砍伐、運輸和燃燒一棵樹需要數周的時間，而種植一棵樹則需要數十年，年輕的樹木對大氣中的二氧化碳吸收能力遠低於成熟的樹木。如果我們想依賴BECCS來減少碳排放，就需要以更快的速度種植更多的樹木。
Harnessing plants’ ability to remove CO₂ by photosynthesis is the best carbon capture technology in the world. It takes weeks to cut down, ship and burn a tree, but decades to grow one. Younger trees suck far less CO₂ from the atmosphere than an older tree. If we want to rely on BECCS to cut our carbon emissions, we need to plant more trees at a faster rate.
這種生質能源需要大片土地，受保護森林中為了生產木屑而進行的砍伐已經對野生動植物構成威脅。在英國的生質能源供應鏈中，對於受保護的森林棲息地進行砍伐等有害作法相當普遍，而這些森林是濒危和稀有野生動物的家園。總之，關於BECCS仍然存在許多不確定性，需要進行更深入的研究和計算其效益。
Huge amounts of land will be needed for this bioenergy. Wildlife is already at risk by timber harvesting for woodchips in protected forests. Harmful practices such as logging in sensitive and protected forest habitats, home to threatened and rare wildlife, are widespread in the UK biomass supply chain. In short, there are still many uncertainties around BECCS – and some proper maths to be done about its benefits.