Coal gasification: The clean energy of the future?

Turning coal into gas is not as environmentally friendly as it sounds

Dirty it may be, but coal is cheap.

For this simple reason, it remains the world's main source of power, providing a quarter of our primary energy and more than 40% of our electricity. And it will continue to do so for many years to come.

The challenge, then, is how to harness coal's energy more cleanly. While global attempts to develop carbon capture and storage (CCS) have stalled, a number of countries are looking at different ways to exploit their abundant coal reserves.
Not all are motivated by environmental concerns, but are driven instead by economics and a desire for energy independence.

Old and new

The main technology being used is coal gasification - instead of burning the fossil fuel, it is chemically transformed into synthetic natural gas (SNG).
The process is decades old, but recent rises in the price of gas mean it is now more economically viable. The US has dabbled in the technique, but China is going all out in a bid to satisfy its soaring demand for power and reduce its dependency on imported liquefied natural gas (LNG).
The country's National Energy Administration has laid out plans to produce 50 billion cubic metres of gas from coal by 2020, enough to satisfy more than 10% of China's total gas demand.
Not only does it make economic sense, but it allows China to exploit stranded coal deposits sitting thousands of kilometres from the country's main industrial centres. Transporting gas is, after all, a lot cheaper than transporting coal.

Coal gasification can also help address local pollution problems that have in recent months brought parts of the country to a virtual standstill.

But there are two big problems. First, coal gasification actually produces more CO2 than a traditional coal plant; so not only will China be using more coal, it will be doing so at a greater cost to the environment.

As Laszlo Varro, head of gas, coal and power markets at the International Energy Agency (IEA), says: "[Coal gasification] is attractive from an economic and energy security perspective.
"It can be a nice solution to local pollution, but its overall carbon intensity is worse [than coal mining], so it is not attractive at all from a climate change point of view".

The US has experimented with coal gasification in recent years 

Indeed a study by Duke University in the US suggests synthetic natural gas emits seven times more greenhouse gases than natural gas, and almost twice as much carbon as a coal plant.
The second problem is water use. Coal gasification is one of the more water-intensive forms of energy production, and large areas of China, particularly in the western parts of the country that would host new gasification plants, already suffer from water shortages.
Mr Varro says a recent IEA report concluded that coal and coal gasification plants would use "quite a substantial portion of the available water in China".

Abundant reserves

 

Other countries are looking at different ways to get gas from coal. One method, particularly popular in Australia, is coal-bed methane, a process allowing access to coal deposits that are too deep to mine. Water is sucked out of the seam and the methane attached to the surface of the coal is freed and then collected.

 “Start Quote

We need to get more radical - we need to get to zero carbon”

Dr Harry Bradbury Founder and chief executive, Five Quarter

China, Indonesia and Mozambique are looking at coal-bed methane, while the US and Canada also have abundant reserves.

Very little CO2 is emitted, but the process is not without controversy. Opponents highlight concerns about water contamination, land subsidence and disposing of waste water safely, while the water intensive process sometimes involves fracking.

And yet coal-bed methane has "fundamentally changed the dynamics of the gas industry in Australia," according to Phil Hirschhorn, partner at the Boston Consulting Group's energy practice in Sydney.

He says there are 200 trillion cubic feet of coal-bed methane resources in the country, with projects under construction to liquify and export 25 million tonnes of gas every year - equivalent to 10% of the entire global LNG market.

Clean access

 

A very different way to produce gas from coal is known as underground coal gasification (UCG), a process that has been around since the 19th Century but which has yet to become commercially viable on a grand scale - there is currently one working facility in Uzbekistan and pilot projects in Australia and South Africa.

Heavy pollution has forced China to rethink how it exploits its coal reserves 

According to Julie Lauder, chief executive of the UCG Association, the process is a "new way of harnessing the energy of coal without the usual environmental impacts".

Technological developments and the rising price of gas mean UCG is now a feasible way of accessing the vast resources of coal that are too deep to mine, she says. Indeed, estimates suggest that as much as 85% of the world's coal resources cannot be accessed through traditional mining techniques.

Opening them up to exploitation has potentially disastrous implications for CO2 emissions and climate change, but the industry says these resources can be accessed cleanly.
The process involves pumping oxygen and steam through a small borehole into the coal seam to produce a small and controlled combustion. Unlike coal-bed methane, therefore, the actual coal is converted from a solid state into gas. The hydrogen, methane, carbon monoxide and CO2 is then siphoned off through a second borehole.

According to Dr Harry Bradbury, founder and chief executive of UK clean energy company Five Quarters, this process results in 20% of the CO2 produced from traditional coal mining.

But his company is developing a process that requires no burning of coal, and which combines what Dr Bradbury calls "solid state chemical engineering" with releasing gases that are trapped not just in the coal, but in the surrounding rocks as well. And all of this takes place offshore, relieving concerns about water contamination and subsidence, he argues.

But the real advantage lies in the ability to capture the CO2. "We need to get more radical - we need to get to zero carbon," Dr Bradbury says. "Full carbon capture and storage is absolutely crucial."
This can take place through re-injecting the CO2 back into the coal seams, or by converting the carbon into products such as plastics and graphene, he says.

The UK government has established a working party to investigate the merits of UCG, undoubtedly excited by the vast resources of coal sitting under the North Sea. Other governments are equally keen to exploit new technologies to access their hidden coal seams.

The problem, of course, is that the process depends entirely on wider efforts to develop CCS, efforts that have, so far, singularly failed to find a solution.

Until one is found, any efforts to gasify coal will either remain theoretical or will exacerbate the already grave problem of CO2 emissions. And if recent efforts are anything to go by, we could be waiting a long time.

By Richard Anderson Business reporter, BBC News

Interferensi Cahaya

Interferensi-Eksperimen Celah Ganda oleh Young

Thomas Young mendapatkan bukti untuk sifat cahaya dan dapat mengukur panjang gelombang untuk cahaya tampak. Cahaya dari suatu sumber jatuh pada layar di layar yang terdapat celah S1 dan S2. Apabila cahaya terdiri dari partikel-partikel kecil mungkin akan melihat dua garis terang pada layar yang diletakkan di belakang celah. Tetapi hasilnya serangkaian garis terang seperti gambar 5 yang disebut fenomena interferensi-gelombang. Panjang gelombang tunggal disebut monokromatik.

Gambar 1: Eksperimen celah ganda oleh Young

Pada gambar 1 menunjukkan amplitudo gelombang bergabung untuk membentuk lebih besar atau saling menguat disebut interferensi konstruktif. Apabila satu berkas menempuh jarak ekstra sebesar setengah panjang gelombang dan pada kedua gelombang tepat berlawanan fase saat dilayar. Puncak satu gelombang pada saat yang sama dengan lembah dari gelombang lainnya tergabung menghasilkan amplitudo nol yang disebut interferensi destruktif atau saling menghilang dengan membuat layar menjadi gelap. Sehingga menghasilkan garis terang dan gelap.

Gambar 2: Gelombang air yang melibatkan dua sumber getaran sebagai contoh interferensi konstruktif dan destruktif

 

Lokasi Rumbai ( Fringe )

Gelombang cahaya mengahasilkan rumbai-rumbai pada percobaan Interferensi celah ganda Young.

Gambar 3: Kontruksi geometrik pada celah ganda Young

Gelombang dari celah S1  dan S2 bergabung di titik P dan sesuatu di titik layar C jarak y dari sumbu pusat. Sudut menunjukkan lokasi P. Dengan sudut D>> d dapat diperkirakan sinar r1 dan r2 sejajar pada sudut ke pusat sumbu.

Interferensi dalam Film Tipis

Efek interferensi biasanya diamati dalam film tipis. Seperti pada gelembung sabun atau lapisan oli dalam air. Variasi warna diamati ketika cahaya putih yang dipantulkan dari permukaan depan dan belakang film transparan tipis. Dengan melihat tiga cara dalam perbedaan fase dua gelombang dapat berubah yaitu melalui pemantulan, gelombang berjalan sepanjang lintasan yang panjangnya berbeda, dan melewati media yang indeks refraksinya berbeda.

Gambar 4: Pantulan cahaya dari film air bersabun tersebar pada lingkaran vertical

Gambar tersebut menunjukkan film sabun vertikal yang ketebalannya meningkat karena gravitasi yang membuat film menumpuk. Pada bagian atas sangat tipis sehingga terlihat gelap. Warna utamanya tergantung pada panjang gelombang gelombang di mana cahaya terpantul mengalami interferensi konstruktif untuk ketebalan tertentu. Semakin ke bawah rumbai menyempit dan warnanya tumpang tindih dan memudar. Pada bagian atasnya sangat tipis  pada filmnya sehingga cahaya yang terpantul pada tempat itu mengalami interferensi destruktif membuat bagian tersebut gelap. Pada rumbai interferensi berwarna menutupi sisanya tetapi diacak pada lingkaran dari cairan dalam film secara bertahap tertarik turun oleh gaya gravitasi.

Interferensi terhadap Pengalih Warna Uang Kertas

Tinta pengalih warna terbuat dari berlapis-lapis serpihan beberapa film tipis yang mengapung pada tinta biasa dengan menunjukkan suatu penampang melintang dari lapisan tinta digunakan pada berbagai mata uang kertas.

Gambar 5: Tinta pengalih warna terbuat dari berlapis-lapis serpihan film

Sumber: Halliday, Fisika Dasar 2

Gambar 6 : Cahaya menembus lima lapisan

Sumber: Halliday, Fisika Dasar 2

Dalam mata uang kertas tersusun berlapis-lapis serpihan lapisan tipis khrom (Cr), magnesium fluoride (MgF₂), dan aluminium (Al). Setiap lapisan memiliki fungsi yang berbeda-beda seperti pada Cr berfungsi sebagai cermin yang lemah, Al sebagai cermin yang lebih baik, dan lapisan MgF₂ berfungsi seperti film sabun. Terdapat hasil cahaya yang dipantulkan ke atas dari setiap batas lapisan kembali melewati tinta biasa dan kemudian mengalami interferensi pada mata pengamat. Jadi dengan mengubah sudut pandang, pengamat dapat mengalihkan warnanya.

How do you dismantle a nuclear submarine?

(Credit: AFP/Getty Images)

When nuclear-powered submarines reach the end of their lives, dismantling them is a complicated and laborious process. Paul Marks investigates.

Nuclear submarines have long been a favourite in popular fiction. From movies such as The Hunt for Red October to long-running TV series like Voyage to the Bottom of the Sea, they have always been portrayed as awesome instruments of geopolitical power gliding quietly through the gloomy deep on secret, serious missions.

An aquarium of radioactive junk — The Kara Sea, a submarine graveyard

But at the end of their useful lives the subs essentially become floating nuclear hazards, fizzing with lethal, spent nuclear fuel that's extremely hard to get out. Nuclear navies have had to go to extraordinary lengths to cope with their bloated and ageing Cold War fleets of hunter-killer and ballistic missile nuclear subs.

(Credit: Science Photo Library)

As a result, some of the strangest industrial graveyards on the planet have been created – stretching from the US Pacific Northwest, via the Arctic Circle to Russia’s Pacific Fleet home of Vladivostok. These submarine cemeteries take many forms. At the filthy end of the spectrum, in the Kara Sea north of Siberia, they are essentially nuclear dumping grounds, with submarine reactors and fuel strewn across the 300m-deep seabed. Here the Russians appear to have continued, until the early 1990s, disposing of their nuclear subs in the same manner as their diesel-powered compatriots: dropping them into the ocean.
Rusting remains
The diesel sub scrapyard in the inlets around Olenya Bay in north-west Russia's arctic Kola Peninsula is an arresting sight: rusted-through prows expose torpedo tubes inside, corroded conning towers keel over at bizarre angles and hulls are burst asunder, like mussels smashed on rocks by gulls.
The Soviets turned the Kara Sea into "an aquarium of radioactive junk" says Norway’s Bellona Foundation, an environmental watchdog based in Oslo. The seabed is littered with some 17,000 naval radioactive waste containers, 16 nuclear reactors and five complete nuclear submarines – one has both its reactors still fully fuelled.

Russian reactors have been stored in the harbour at Vladivostok (Credit: Bellona Foundation)

The Kara Sea area is now a target for oil and gas companies – and accidental drilling into such waste could, in principle, breach reactor containments or fuel rod cladding, and release radionuclides into the fishing grounds, warns Bellona's managing director Nils Bohmer. Official submarine graveyards are much more visible: you can even see them on Google Maps or Google Earth. Zoom in on America's biggest nuclear waste repository in Hanford, Washington, Sayda Bay in the arctic Kola Peninsula, or the shipyards near Vladivostok and you'll see them. There are row after row of massive steel canisters, each around 12m long. They are lined up in ranks in Hanford's long, earthen pits awaiting a future mass burial, sitting in regimented rows on a Sayda Bay dockside, or floating on the waters of the Sea of Japan, shackled to a pier at the Pavlovks sub base near Vladivostok.
Drained and removed
These canisters are all that remain of hundreds of nuclear subs. Known as "three-compartment units" they are the sealed, de-fuelled reactor blocks produced in a decommissioning process perfected at the US Department of Defense's Puget Sound Naval Shipyard in Bremerton, Washington.
It’s a meticulous process. First, the defunct sub is towed to a secure de-fuelling dock where its reactor compartment is drained of all liquids to expose its spent nuclear fuel assemblies. Each assembly is then removed and placed in spent nuclear fuel casks and put on secure trains for disposal at a long-term waste storage and reprocessing plant. In the US, this is the Naval Reactor Facility at the sprawling Idaho National Laboratory, and in Russia the Mayak plutonium production and reprocessing plant in Siberia is the final destination.

(Credit: Getty Images)

Although the reactor machinery – steam generators, pumps, valves and piping – now contains no enriched uranium, the metals in it are rendered radioactive by decades of neutron bombardment shredding their atoms. So after fuel removal, the sub is towed into dry dock where cutting tools and blowtorches are used to sever the reactor compartment, plus an emptied compartment either side of it, from the submarine's hull. Then thick steel seals are welded to either end. So the canisters are not merely receptacles: they are giant high-pressure steel segments of the nuclear submarine itself – all that remains of it, in fact, as all nonradioactive submarine sections are then recycled. Russia also uses this technique because the West feared that its less rigorous decommissioning processes risked fissile materials getting into unfriendly hands. At Andreeva Bay, near Sayda, for instance, Russia still stores spent fuel from 90 subs from the 1960s and 1970s, for instance. So in 2002, the G8 nations started a 10-year, $20bn programme to transfer Puget Sound's decommissioning knowhow to the Russian Federation. That involved vastly improving technology and storage at their de-fuelling facility in Severodvinsk and their dismantling facility, and by building a land-based storage dock for the decommissioned reactors.
Floating menace
Safer land-based storage matters because the reactor blocks had been left afloat at Sayda Bay, as the air-filled compartments either side of the reactor compartment provide buoyancy, says Bohmer. But at Pavlovks, near Vladivostok, 54 of the canisters are still afloat and at the mercy of the weather.
Decommissioning this way is not always possible, however, says Bohmer. Some Soviet subs had liquid metal cooled reactors – using a lead-bismuth mixture to remove heat from the core – rather than the common pressurised water reactor (PWR). In a cold, defunct reactor the lead-bismuth coolant freezes, turning it into an unwieldy solid block. Bohmer says two such submarines are not yet decommissioned and have had to be moved to an extremely remote dockyard at Gremikha Bay – also on the Kola Peninsula – for safety's sake.

When nuclear submarines reach the end of their lives, some of their hulks remain dangerously radioactive (Credit: Science Photo Library)

Using the three-compartment-unit method, Russia has so far decommissioned 120 nuclear submarines of the Northern Fleet and 75 subs from its Pacific Fleet. In the US, meanwhile, 125 Cold War-era subs have been dismantled this way. France, too, has used the same procedure. In Britain, however, Royal Navy nuclear subs are designed so that the reactor module can be removed without having to sever compartments from the midsection. "The reactor pressure vessel can be removed in one piece, encased, transported and stored," says a spokesman for the UK Ministry of Defence. However Britain's plans to decommission 12 defunct submarines stored at Devonport in the south of England and seven at Rosyth in Scotland won't happen any time soon as the government still has to decide which of five possible UK sites will eventually store those pressure vessels and spent fuel. This has raised community concerns as the numbers of defunct nuclear-fuelled subs is building up at Devonport and Rosyth, as BBC News reported last year.
Water fears
Environmental groups have also raised concerns about fuel storage in the US. The Idaho National Lab has been the ultimate destination for all US Navy high-level spent fuel since the first nuclear sub, USS Nautilus, was developed in 1953. "The prototype reactor for the USS Nautilus was tested at INL and since then every scrap of spent fuel from the nuclear navy has ended up in Idaho. It is stored above the upstream end of the Snake River Aquifer, the second largest unified underground body of water on the North American continent," says Beatrice Brailsford of the Snake River Alliance, an environmental lobby group.
"The spent fuel is stored above ground, but the rest of the waste is buried above the aquifer and that practice may continue for another half century. It is a source of concern for many people in Idaho." It's not only the aquifer's fresh water that's at risk: the state’s signature crop, potatoes, would also be affected.

(Credit: Science Photo Library)

Even with high security, radioactive material can occasionally escape – sometimes in bizarre ways. For instance both INL and Hanford have suffered unusual radiation leaks from tumbleweeds blowing into waste cooling ponds, picking up contaminated water, and then being blown over the facility's perimeter by the wind. The expensive, long-term measures that have to be taken to render a defunct nuclear sub safe don’t seem to deter military planners from building more vessels. "As far as the US is concerned there is no indication that the Navy believes nuclear submarines have been anything less than a stellar success and replacements for the major submarine classes are in the works." says Edwin Lyman, nuclear policy analyst at the Union of Concerned Scientists, a pressure group, in Cambridge, Massachusetts.

The Russian Navy is planning to launch several new submarines (Credit: Science Photo Library)

The US is not alone: Russia has four new nuclear subs under construction at Severodvinsk and may build a further eight before 2020. "Despite limited budgets Russia is committed to building up its nuclear fleet again," says Bohmer. China is doing likewise.