Clean Coal Technology: A Novel Process for the Combustion of Coal Using an Oxygen Carrier

洁净煤技术：利用氧载体燃烧煤炭的新工艺

• 批准号: EP/D055725/1
• 负责人: John Dennis
• 金额: $ 33.23万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FD055725%2F1
• 关键词: Clean; Coal; Technology; Novel; Process

The global supply of electricity accounts for ~38% of total anthropogenic carbon emissions to the atmosphere or ~2,400 Mte/y (carbon basis), a figure projected to exceed 4,000 Mte/y by 2020. Globally, coal generates the largest share of world electricity production (39% of total delivered energy) followed by renewables (principally hydroelectricity) (20%), nuclear (17%), gas (15%) and oil (10%). Electricity production will increase by ~80% over the period 2000 to 2020, with the fraction generated from coal remaining at ~39%, due to increased exploitation of coal in India and China and steady growth in the USA. In the U.K., the most recent White Paper only envisages a future for coal provided ways can be found materially to reduce its carbon emissions , which therfore requires the sequestration of the CO2 arising from the combustion of the coal, or fuels derived from it, in the earth. The cost of sequestration is small (~ $4-8/ te C) compared to the costs of separation of CO2 from typical flue gases (~ $100 - 200/te C)so that such disposal only approaches viability if the CO2 is available in almost pure form, largely free of nitrogen and other inert gases.We wish to use chemical looping for the in situ gasification and combustion of coal in a process to produce CO2 and steam as pure products, without significant contamination by N2. In our proposed scheme, there would be one reactor, containing a bubbling fluidised bed of oxygen carrier, most likely a Cu-based oxide on a titania or alumina support, the durability of which has been demonstrated by other workers. The reactor would be operated in a cycle of three consecutive periods, t1, t2 and t3. During t1, the bed would be fluidised by steam, (or steam and CO2) and coal would be fed steadily to the bed, the temperature of which would be ~ 800 - 1000 C. Two events would occur:(1) the coal would undergo gasification (endothermic) by the steam to yield a synthesis gas containing CO and H2 (plus smaller amounts of CH4 and higher hydrocarbons): C(s) + H2O(g) = CO(g) + H2(g) (enthalpy of reaction: +131 kJ/mol),(2) the syngas would react with the surrounding CuO particles to give CO2 and steam by: CuO(s) + H2(g) = Cu(s) + H2O(g) and CuO(s) + CO(g) = CO2(g) + Cu(s) (enthalpies of reaction -86 kJ/mol and -127 kJ/mol, respectively).Copper has the only oxides which give exothermic reactions in (2); the heat produced exceeds that needed for the endothermic gasification reaction in (1). In effect, the metal oxide has been used in place of air, or cryogenically-produced O2, so that the products of combustion do not contain N2. Of course, this system can only function down to a certain degree of reduction of the metal oxide. Thus, after time t1, the feed of coal ceases and the remaining inventory of bed carbon is allowed to gasify and combust for a further period of time, t2, until the inventory is sufficiently small. At the end of t2, the bed is fluidised by air instead of steam for a period of time, t3, during which the reduced metal oxide carrier is regenerated in Cu + 0.5O2 = CuO (enthalpy of reaction -156 kJ/mol Cu). During t3 some carbon will be burnt off, originating either from coked metal oxide or from residual carbon inventory remaining after t2, so that there would be a small release of CO2 with the regenerating air, but this would be very much less than that emitted by direct combustion of the coal in air. Once the metal oxide has been regenerated, the cycle starts again at t1. Thus, the concept enables coal to be burnt cleanly with a rather smaller reduction in thermal efficiency than is obtained with other schemes for isolating the CO2, using e.g. cryogenically-separated oxygen from air.

全球电力供应占大气中人为碳排放总量的约38%，或约2,400吨/年(碳基)，预计到2020年这一数字将超过4,000吨/年。在全球范围内，煤炭在世界发电量中所占份额最大(占总发电量的39%)，其次是可再生能源(主要是水力发电)(20%)、核能(17%)、天然气(15%)和石油(10%)。由于印度和中国的煤炭开采量增加以及美国的稳定增长，发电量将在2000年至2020年期间增长约80%，其中来自煤炭的比例将保持在约39%。在英国，最新的白皮书只设想了煤炭的未来，只要能找到实质性的方法来减少煤炭的碳排放，因此需要将煤炭或从煤炭获得的燃料在地球上燃烧产生的二氧化碳封存起来。与从典型烟道气中分离二氧化碳的成本(大约100-200美元/TE C)相比，封存的成本很小(约4-8美元/TE C)，因此只有当二氧化碳以几乎纯的形式存在，基本上不含氮和其他惰性气体时，这种处置才接近可行。我们希望使用化学循环在一个过程中对煤炭进行原位气化和燃烧，以产生二氧化碳和蒸汽作为纯产品，而不会受到明显的氮气污染。在我们提议的方案中，将有一个反应器，其中包含一个鼓泡的流态化氧气载体床，最有可能是二氧化钛或氧化铝载体上的铜基氧化物，其耐用性已被其他工作人员证明。该反应堆将以三个连续周期运行，即T1、T2和T3。在T1期间，床层将被水蒸气(或水蒸气和二氧化碳)流态化，煤将稳定地进入床层，其温度将为~800-1000℃。将发生两个事件：(1)煤将被水蒸气气化(吸热)，生成含有CO和H2(加上少量CH4和较高碳氢化合物)的合成气：C(S)+H2O(G)=CO(G)+H2(G)(反应热：+131kJ/mol)，(2)合成气与周围CuO反应生成CO_2和水蒸气的反应条件为：CuO(S)+H_2(G)=Cu(S)+H_2O(G)和CuO(S)+CO(G)=CO(G)+Cu(S)(反应热分别为-86kJ/m o l和-127k J/m o l)。产生的热量超过(1)中吸热气化反应所需的热量。实际上，金属氧化物已经被用来代替空气，或低温产生的氧气，因此燃烧的产物不含氮气。当然，这一体系只能起到一定程度的还原金属氧化物的作用。因此，在时间t1之后，停止给煤，并且允许床碳的剩余库存气化和燃烧进一步的时间t2，直到库存足够小。在T2结束时，用空气代替水蒸气使床流态化一段时间t3，在此期间，还原的金属氧化物载体在Cu0+0.5O2=CuO(反应热-156kJ/摩尔铜)中再生。在T3期间，一些碳将被燃烧掉，这些碳来自于焦化的金属氧化物或T2之后剩余的碳库存，因此再生空气将有少量二氧化碳释放，但这将比煤炭在空气中直接燃烧所排放的要少得多。一旦金属氧化物被再生，循环在t1再次开始。因此，这一概念使煤炭能够清洁燃烧，而热效率的下降比其他分离二氧化碳的方案要小得多，例如使用从空气中低温分离的氧气。

项目成果

Kinetics of the chemical looping oxidation of H2 by a co-precipitated mixture of CuO and Al2O3

• DOI: 10.1016/j.cherd.2010.08.003
• 发表时间: 2011-09
• 期刊: Chemical Engineering Research & Design
• 影响因子: 3.9
• 作者: S. Chuang;J. S. Dennis;A. Hayhurst;S. Scott