Circulating fluidized bed combustion technology offers a way to reliably and cleanly convert Turkey’s low quality lignite into power, argue Bob Giglio and Boguslaw Krzton
Turkey’s GDP is predicted to grow nearly 60 per cent over the next five years, ranking as one of the fastest growing economies in the world. This high level of economic growth, coupled with Turkey’s strongly growing industrial base, is expected to drive electricity demand growth from 95 TWh to 132 TWh, nearly a 40 per cent increase over the same five-year period. To keep up with this insatiable need for power, Turkey’s energy imports are expected to grow considerably, causing both an energy security and economic burden concern.
In 2016, 33 per cent of Turkey’s electric power was produced from imported natural gas, half of that from Russia and more than half of its coal and lignite power was from imported hard coal. Only 16 per cent of Turkey’s total electric power was generated using local lignite.
|When commissioned in late 2018, the 2 x 255 MW Soma Kolin Power Plant will become the largest CFB plant in Turkey. Source: Sumitomo SHI FW|
The situation is even worse when looking at the total primary energy demand of the country, as only 30 per cent is sourced from domestic sources such as hydro, lignite, and renewables. Said another way, 70 per cent of Turkey’s economy is fueled by imported energy, costing Turkey $27.2 billion in 2016.
Turkey has 17.2 billion tonnes of proven lignite reserves, enough to power its growing economy well into the future. But ironically, over the past five years, imported coal capacity grew 3.5 times more than lignite power capacity (4.9 GW vs 1.4 GW). Policymakers in Turkey want to change this to improve Turkey’s energy security while lowering its energy cost.
Tapping into Turkey’s massive lignite reserves is a key part of Turkey’s Vision 2023 energy plan, timed to mark the 100th anniversary of the founding of the Republic. The plan calls for increased use of lignite for meeting rising electricity demand while improving Turkey’s energy security. The plan calls for more than doubling domestic lignite power capacity over the next 10 years, amounting to 10 GW of new power capacity from Turkey’s lignite.
The good news is that Turkey’s huge lignite reserves can solve its energy security problem. The bad news is that 68 per cent of the total lignite reserves in Turkey have low calorific value (1.000–2.000 kcal/kg) which is a very challenging fuel for today’s conventional coal power plant technology.
It is no coincidence that Turkey has not turned to its lignite reserves earlier, and you don’t need to look very hard to find power plants that struggle every day to burn its low quality lignite.
|Figure 1: Annual average plant availability of SFW CFBs and coal plant fleets.|
Right time for the right technology
Today, the timing couldn’t be better for aligning the right technology to Turkey’s energy strategy. Over the last 40 years, circulating fluidized bed (CFB) combustion technology has grown in both scale and experience. Today, CFB has become the best choice for reliably and cleanly converting low quality fuels into power.
In a broader sense, CFB’s fuel flexibility and ability to control pollution during the burning process has caused many utilities, IPPs and developers to choose CFB technologies for their new coal, lignite, biomass, petcoke, and waste-to-energy plants. But for Turkish lignite, the key words are ash and moisture, since Turkey’s low quality lignite has the highest levels of them, in the 30–50 per cent range. Moreover, the ash has very low melting temperatures making quite a slagging mess in conventional boilers.
In a conventional pulverized coal (PC) or PF boiler, this ash melts causing slagging and fouling throughout the boiler. These boilers are oversized, use a lot of soot blowing, and are frequently down for maintenance, resulting in elevated plant capital and operating cost and lower plant reliability.
The CFB technology avoids all these pitfalls, since the ash doesn’t melt due to its flameless low temperature combustion process. Instead, the ash is circulated throughout the boiler, cleaning the boiler’s heat transfer surfaces and evenly spreading the fuel’s heat while completely combusting the fuel.
This one difference is the main reason that CFB boilers can achieve reliability levels unreachable by conventional PC boilers. Figure 1 (see page 28) shows average annual plant reliabilities between plants with SFW CFBs as compared to coal plant fleets in several world regions reported by multiple sources.
There are many other advantages of the CFB combustion process. For instance, the CFB does not need fuel dryers, pulverizers, conduits, or burners. Instead, the fuel needs to be only coarsely crushed and dropped into chutes in the lower furnace. Most of the time, expensive SCR DeNOx or downstream FGD DeSOx systems are not needed to meet permitted emission limits.
Combustion stability and efficiency is another area where CFB excels. Since the CFB circulates the fuel over and over in a bed of hot solids, it completely burns all fuels, even the most difficult low volatile fuels, like anthracites and petcokes. Fuel particles can stay in the CFB hot loop for as long as 30 minutes as compared to a PC with burning times of only three-to-four seconds.
Further, the bed of hot solids in the CFB provides a large thermal inertia. This makes the combustion process very stable, allowing wide variations in fuel properties without upsetting boiler emissions or steam capacity. In contrast, the PC burning process has no thermal inertia since the fuel is instantly converted to a hot gas and molten ash particles.
The Soma Kolin project
The new Soma power plant is located in Soma Basin, 135 km north of Izmir. The owner, Hidro-GEN Enerji Ithalat Ihracat Dagitim ve Ticaret, is a subsidiary of Turkish construction company Kolin Holding.
Hidro-GEN is following through with its plan to open the new lignite mine and build the 510 MW lignite CFB power plant designed around SFW’s CFB boiler technology. When operational in 2018, the plant will become Turkey’s largest lignite power plant utilizing CFB boiler technology. The plant is configured with 2 x 255 MW CFB boilers and steam turbine generators.
The contract for the supply of two CFB boiler islands with auxiliary equipment and the two CFB scrubber systems was awarded to SFW in January 2014 by EPC contractor Harbin Electric International. A number of local Turkish subcontractors are working on the plant site in different areas of the power plant and mine.
After a short project delay related to final site selection approvals, construction began on the plant in January 2016. Boiler hydro is scheduled for late 2017 and plant commercial operation is scheduled for mid-2018.
Building a lignite-burning power plant in the Soma region makes good economic and fuel security sense, but the challenge was finding the right technology to fire this very low quality lignite with a higher heating value of 6770 kJ/kg (1618 kcal/kg), containing 23.3 per cent moisture, 42.9 per cent ash and 1.2 per cent sulphur.
Each CFB is a natural circulation steam generator with reheat rated at 255 MWe (545 MWth). Main steam conditions of the CFBs are 173 bar abs/565oC with reheat conditions of 53 bar abs/565oC. The CFB boiler design includes steam-cooled solid separators and special INTREX heat exchangers, which are utilized as the final superheating stage. Due to the high ash content in the fuel, the CFBs are equipped with high capacity drum coolers which drop the bottom ash into redundant drag chain conveyors.
|Figure 2. Soma Kolin design|
Since Turkey’s government has been considering accession to the European Union, flexibility in plant emissions was important to the Kolin Group, the owner or the plant. They wanted to have the flexibility to achieve a wide range of stack emissions, while at the same time allowing a wide range of fuel sulphur contents expected from the lignite mine over the long term.
Currently, Turkish environmental regulation is based on Europe’s large combustion plant directive (LCP) with SOx/NOx/PM emission limits of 200/200/30 mg/Nm3.
But current EU environmental rules are based on the Industrial Emissions Directive levels which recently have been updated by the BREF BAT document. The BREF lowers yearly SOx limits down to the 10–75 mg/Nm3 range, NOx down to the 50–85 mg/Nm3 range and PM down to the 2–5 mg/Nm3 range for large new coal and lignite plants. In addition, the BREF adds strict limits in the 1–3 mg/Nm3 range to several new pollutants, such as, HCl, HF, Hg, and NH3.
For this flexibility, a CFB ‘polishing’ scrubber (CFBS) was added behind the CFB boiler for the Soma Kolin plant. This will allow the CFB ash to be used as a reagent in the CFBS to reduce emissions while also reducing the use of expensive reagents such as hydrated lime.
Two ash hydrators on-site will condition the recycled fly ash before injection into the absorber. The CFBS will also capture HCl, HF, Hg, and NH3 so the plant will be able to comply with the EU’s strict BREF limits providing multi-pollutant emission control very economically.
The Soma Kolin project is very important to Turkey as well as other countries with large resources of low quality coals and lignites. CFB technology is the best choice for tapping into Turkey’s vast lignite reserves, as underscored by the project.
The success of Soma Kolin will encourage countries, such as India, Germany, Thailand and Pakistan to reconsider their plans for using their low quality indigenous fuels for secure, affordable and clean power.
Bob Giglio is Senior Vice-President for Global Business Strategy, and Boguslaw Krzton is Vice-President for Strategic Business Development in Central and Eastern Europe and Turkey, at Sumitomo SHI FW.