JP2004529056A - Method for producing hydrogen and its use - Google Patents

Abstract

Method for producing hydrogen gas. Hydrogen gas is produced by steam reduction using a metal / metal oxide pair that removes oxygen from water. The vapor is contacted with a molten metal mixture that includes a first reactive metal, such as iron, dissolved in a diluting metal, such as tin. The reactive metal is oxidized to a metal oxide while generating hydrogen gas, and the metal oxide is then reduced to the metal to produce more hydrogen without significantly transferring the metal or metal oxide to the second reactor. The reactor (400) includes a refractory side wall (402) adapted to contain a molten metal mixture (404). When steam is introduced from the lance (408), the iron in the metal mixture (404) is oxidized to iron oxide, which rises and accumulates in the slag layer (406). A gas product (416) containing hydrogen gas mixed with steam is withdrawn from the outlet (410).

Description

【００３８】
６６０℃でのスズの熱力学的な蒸気必要量は１２００℃での鉄の熱力学的な蒸気必要量に略等しい。しかし、６５０℃でスズを反応性金属として使用して水素を製造するのは、速度論（すなわち反応速度）が非常に劣り、したがって非常に長い滞留時間（すなわち蒸気がスズと接触している時間）が必要となるので、実際的ではない。
【００３９】
１２００℃ではスズおよび鉄の反応速度は優れている。しかし、スズの蒸気必要量は鉄よりもはるかに多い。本発明によれば、蒸気が反応性金属と接触する滞留時間は希釈用金属を使用することによって増加する。説明のために、純粋なスズと比較した、１２００℃の温度および種々の圧力における本発明の実施形態の溶解鉄（スズ中に鉄５０重量％）の熱力学的蒸気必要量および名目滞留時間の比較を表１および２に示す。表１は１２００℃で１トンの水素を製造するのに必要な蒸気の総量を示す。
【００４０】
【表１】

【００４１】
表２は４．４３９トンの水素の製造速度における名目滞留時間を示す。
【表２】

【００４２】
表１および２のデータから、純粋なスズ系は本発明による溶解鉄系よりも水素を製造するのに多くの蒸気を必要とすることが明らかである。また、表２は蒸気と反応することのできるスズの名目滞留時間が、蒸気と反応することのできるスズに溶解した鉄の名目滞留時間よりもかなり短いことを示している。名目上のまたは見かけの滞留時間は、蒸気（工程の反応物）が使用する反応性金属の量で占められた空間を通り抜けることのできる時間である。表２において、溶融体積は、水素製造速度が４．４３９トン水素／時間であるときに化学量論的に必要な金属量である。この時間中、理想的には水素は熱力学的なｐＨ₂／ｐＨ₂Ｏの比に対応する量が製造される。化学量論的な量よりも多い反応性金属の量によって名目滞留時間を増加させることが可能であるが、結果は反応器のサイズとコストが増加する。また、圧力を高くすることは蒸気と反応性金属間で可能な反応時間を増加させるが、しかしコストの追加となる。
【００４３】
したがって、本発明による希釈用金属に溶解した反応性金属を用いる１つの重要な利点は、反応性金属の質量に関して反応器中での蒸気の滞留時間が増加することである。すなわち、一定質量の鉄は純粋な鉄として第１の体積を占めようが、鉄がスズなどの希釈用金属と５０重量％の混合物として存在すれば、同じ質量の鉄はその体積の約２倍に分布するであろう。
【００４４】
図１はハリクマールＫ．Ｃ．ら、Calphad、第２０巻、２号、１３９〜１４９ページ、１９９６年（非特許文献３）から翻案した鉄とスズの相図を示す。図１から、鉄（反応性金属）をスズ（希釈用金属）に加える１つの効果は、鉄の溶融温度をかなり低くすることであることが判る。液相の金属混合物は、約４８．７重量％のスズおよび５１．３重量％の鉄の溶融組成物で、１５３８℃（純鉄）から約１１３４℃へ下がる。
【００４５】
一実施形態によれば、金属混合物は図１の液相線ＡＣよりも上の温度に保つことが好ましい（例えば約１１３４℃）。しかしあまり高い金属−蒸気反応温度には運転コストが大きく加わる。図１に示した完全に溶融した鉄／スズ系では、溶融物を液相の温度１１３４℃以上の温度、より好ましくは少なくとも約１２００℃の温度に保たなければならない。適正に経済的であるために、温度は約１５００℃以上であってはならず、より好ましくは約１４００℃以上であってはならない。完全に溶融した鉄／スズ金属混合物の特に好ましい温度範囲は、約１２００℃〜１３００℃である。１２００℃で、約５０重量％の鉄が十分な過熱（superheat）でスズに溶解し、鉄の酸化時、混合物は溶融状態を保つ。また、１２００℃での純粋な水素を生成する、蒸気とスズに溶解した液体鉄の間の反応は非常に激しく、反応速度は優れている。さらに、１２００℃での蒸気／鉄系の熱力学は比較的良好で、水素トン当たり約１２．２トンの蒸気（水素１モル当たり蒸気１．３７モル）を必要とするだけである。
【００４６】
この実施形態によれば、金属混合物は溶融金属混合物中に最初に少なくとも約３重量％の鉄を含むことが好ましく、少なくとも約１０重量％の鉄がより好ましく、少なくとも約２０重量％の鉄がさらに好ましく、約５０重量％の鉄がさらにより好ましい。さらに、溶融金属混合物中の鉄の量は約８５重量％を超えないことが好ましく、約８０重量％を超えないことがより好ましい。好ましい実施形態においては、金属混合物の残りは実質的にスズからなる。したがって、系中のスズの量は約９７重量％を超えないことが好ましく、約９０重量％を超えないことがより好ましく、約８０重量％を超えないことがさらに好ましい。溶融金属混合物は少なくとも１５重量％のスズを含むことが好ましく、少なくとも約２０重量％のスズを含むことがより好ましい。
【００４７】
本発明は溶融金属混合物の存在を必要としているが、一実施形態においては、粒子状などの不溶相が溶融金属混合物に分散されていてもよい。この溶融金属混合物と不溶相との組み合わせをスラリーと称する。一実施形態によれば、蒸気が溶融金属混合物および固体の第２相を含むスラリーと接触される。固体の第２相は反応性金属を含有する粒子を含み、溶融金属混合物に追加の反応性金属を供給する。粒子は金属性粒子（例えば酸化物粒子ではない）であることが好ましい。例えば、スラリーは鉄で飽和されている鉄／スズ溶融物中に、鉄に富む金属性粒子を含むことが可能である。蒸気還元工程が進むと、溶解した鉄は鉄の酸化によって溶融金属混合物から除去され、鉄に富む粒子からの追加の鉄が溶融金属に溶解して、鉄で飽和されたスラリーの溶融金属部を保つ。
【００４８】
図１の相図を参照すれば、点Ａ（１１３４℃でＦｅ８３．３重量％）、点Ｂ（１１３４℃でＦｅ８４重量％）、点Ｃ（８９５℃でＦｅ１２重量％）、および点Ｄ（８９５℃でＦｅ３重量％）によって区画された二相領域における組成物は、総量約３重量％〜８４重量％の鉄を有する鉄／スズ溶融物を含み、鉄の一部は溶融物中に分散した鉄に富む金属性粒子である。約８９５℃〜約１１３４℃の間の所定の温度で鉄が酸化によって溶融金属から除去されると、鉄に富む粒子からの追加の固形鉄が溶解し、それによって溶融物中の鉄のレベルを固形鉄がなくなるまでバルクの飽和状態に維持する。この鉄に富む粒子から生じる鉄による酸化されることのない鉄の置換によって、鉄の活量が高く保たれ、すなわち、水素の製造が最大になる。例えば、約９５０℃の温度、および約５０重量％の総鉄量で、溶融金属混合物は系中に約４重量％の溶解した鉄を含むであろう。溶解した鉄が酸化されると、鉄に富む粒子からの追加の金属鉄が溶解し、溶融物中の溶解鉄を４重量％に維持する。鉄に富む粒子の溶解によって鉄の活量は変化しない。
【００４９】
したがって、この実施形態によれば、溶融金属混合物と鉄含有粒子からなるスラリーは１１３４℃以下で少なくとも８９５℃、より好ましくは約９００℃〜１１３４℃の間の液相温度に維持される。
【００５０】
その方法の１つの利点は鉄の活量が、一定、実際には１に近い値に保たれ、したがって水素の製造速度が蒸気還元工程を通じて一定および最大に保たれることである。
反応性金属が一定の活量であることの望ましい効果は、工程が図１のミシビリティギャップ領域内で行われるならば観察されるであろうが、しかし鉄の活量は１よりも若干小さい。
【００５１】
排ガス中の水素の分圧、反応温度、および溶融金属組成物中の鉄の重量％の間には熱力学的な関係が存在する。鉄の「活量（activity）」と称される熱力学的な量は鉄の濃度の関数として変化し、排ガス中の水に対する水素の比率に大きな影響を与える。水素の製造は、反応相と平衡な第２相を用いることにより、広い組成物領域にわたって高い鉄の活量が確立される相領域内で運転することによって最大となる。これは図１の線ＡＣの上の液相−液相領域、同じく線ＡＣの下、および線ＡＢの右の固相−液相領域の両方にあてはまる。しかし、本発明は鉄に富む液相での実施を排除するものではない。
【００５２】
図２は溶融金属混合物中の鉄含有量の関数で示した排ガス（off-gas）中の水素のレベルの関係を示している。図２は１２２５℃での反応の熱力学に基づいて計算したものである。鉄含有量が２０重量％から１０重量％に下がると、水素製造の速度が急速に減少することが明らかである。図３は温度および鉄含有量の関数としての水素製造を示している。
【００５３】
約２０重量％以下の鉄レベル、および約１１３４℃以上の温度で、水素の製造能力は減少する。その理由は、（１）ｐＨ₂／ｐＨ₂Ｏが大きく低下する、（２）ガス流（すなわち、蒸気と酸化金属の還元剤）を切り替える前に短い時間しかないためである。
【００５４】
このようにして、蒸気が溶融金属混合物と接触して水素を発生し反応性金属を酸化金属に変換する。蒸気は良好な攪拌と溶融金属混合物との接触を促進するようにして溶融金属混合物と接触させる。例えば、蒸気は先端部浸漬ランスからの注入、または反応器の底部に配置した多孔質セラミック拡散器からの注入によって溶融金属混合物と接触させることが可能である。この件に関する好ましい反応器システムは以下に説明する。反応器の温度は流入する蒸気の温度および量を制御することによって、および／または反応器に酸素を加えることによって制御し、実質的に一定の温度に維持することが可能である。
【００５５】
蒸気還元反応器は、反応器中での適切な滞留時間が必要であれば、上述のように高圧に維持することが可能である。例えば、少なくとも約１５．３気圧（２２５ｐｓｉ、１５５０３ヘクトパスカル）に維持することが望ましいであろう。僅かに高くした圧力もまた、水素ガス流に移動のための十分な圧力（例えばライン圧力約２００ｐｓｉ（１３７８０ヘクトパスカル）を提供する上で有益である。しかし、圧力を非常に高くすると資本コストを増加させるため、蒸気還元反応器中の圧力は約６００ｐｓｉ（４１３４１ヘクトパスカル）以下であることが好ましく、約２２５ｐｓｉ（１５５０３ヘクトパスカル）以下であることがさらに好ましい。
【００５６】
本発明によれば、スラグ層が溶融金属混合物上に維持される。スラグ層は酸化鉄の反応器からの流出防止を含む多くの利点を提供する。蒸気還元反応器中の温度は、金属混合物上に形成されるスラグ層を組成物の広い範囲にわたって溶融状態に維持するのに十分でなければならない。反応性金属が酸化されると、金属混合物中の反応性金属の濃度が減少するが、反応性金属が酸化されても金属混合物は溶融状態に維持されなければならない。図１に関して説明した溶融金属の組成物範囲と同様に、十分なスラグの流動性と反応性を確保するために必要な好ましいスラグの組成、および発泡の防止は、所定の温度で必要に応じて調節することが可能である。例えば、フラックスを反応器に加えてスラグの特性を調節することが可能である。フラックス系の１つはＳｉＯ₂、ＦｅＯ、ＣａＯ、ＭｇＯ、Ｎａ₂Ｏ、およびＫ₂Ｏの液体表面であると言える。しかし、硫黄および他のカチオンをこのスラグまたは他のスラグに取り込み、スラグの十分な化学的性質を確実にすることも可能である。
【００５７】
蒸気還元によって発生する酸化金属（例えばウスタイトおよび／またはマグネタイト）は反応器中でスラグによって都合良く捕捉する（溶解または分散）ことが可能である。好ましい温度で、酸化鉄は金属混合物よりも軽いスラグ中に取り込まれる。したがって、溶解した鉄が溶融金属混合物からなくなると、溶融金属を通って酸化鉄が上昇し、溶融金属の頂上のスラグ層に寄与する。反応性金属が蒸気と反応して生成した酸化物は、溶融金属混合物の密度よりも低い密度を有し、それによって酸化物がスラグ層へと上昇することは、本発明のこの実施形態の１つの利点である。酸化金属の密度が溶融金属混合物よりも少なくとも約１０％低いことが好ましい。これはまた、酸化金属が還元された際に、金属がスラグ層から溶融金属混合物中へ沈下することを可能にする。上述したように、スラグ中の酸化鉄の堆積は、粘度、反応性、発泡性などに関してスラグを好ましい条件に維持するために、ＳｉＯ₂、ＦｅＯ、ＣａＯ、ＭｇＯ、Ｎａ₂Ｏ、Ｋ₂Ｏまたはその混合物などのフラックスの添加を必要とするであろう。
【００５８】
溶融金属混合物は、適切な反応条件を維持するために、適切な反応器内に収容されなければならない。さらに、反応物は良好な攪拌と大きな接触表面積を実現するように供給されなければならない。良好なガス／液体の接触を確立するための適切な高温の反応器は、化学、および特に冶金工業において用いられている。
【００５９】
本発明の好ましい反応器システムは、蒸気を溶融金属中に注入するために先端部浸漬ランス（top-submerged lance）を用いる。その反応器は、スズ鉱石（錫石）からの工業的なスズ製造に用いられてきた。反応物を注入するための先端部浸漬ランスを用いる反応器の例は、フロイド（Floyd）らの米国特許第３，９０５，８０７号（特許文献９）、米国特許第４，２５１，２７１号（特許文献１０）、米国特許第５，２５１，８７９号（特許文献１１）、バルドック（Baldock）らの米国特許第５，２８２，８８１号（特許文献１２）、フロイドらの米国特許第５，３０８，０４３号（特許文献１３）、米国特許第６，０６６，７７１号（特許文献１４）に開示されている。これらの特許の各々はその全体を本願明細書に援用している。その反応器は反応物（例えば蒸気）をマッハ１に近い高速度で溶融金属中に注入し、それによって反応物の良好な攪拌を促進する。
【００６０】
蒸気を注入するランスの組み込まれた反応器を図４に示す。反応器４００は、溶融金属混合物４０４を収容するように適合された耐火側壁４０２を含む。反応器４００内の温度を維持するために、必要ならば、加熱手段（図示せず）を設けてもよい。先端部浸漬ランス４０８は上部壁４１２を貫通して配設され、蒸気を高速で金属混合物中に注入するようになっている。先端部浸漬ランス４０８は、スラグ層４０６の表面の下部でかつ溶融金属混合物４０４とスラグ層４０６の界面の近傍で終端し、蒸気を注入することが好ましい。蒸気がランス４０８を通って導入されると、金属混合物４０４中の鉄が酸化鉄に酸化される。酸化鉄は上昇してスラグ層４０６に堆積する。蒸気と混和した水素ガスを含むガス生成物４１６は、流出口４１０から採収され、その後過剰の蒸気を凝縮して実質的に純粋な水素流を生成することが可能である。
【００６１】
蒸気還元工程は水素製造速度が十分低いレベルまで低下するまで継続される。その後、溶融金属混合物およびスラグを収容する反応器に還元剤が導入され、酸化鉄を金属に還元する。蒸気還元工程を停止し、勤続還元工程を開始する点は、経済的な理由に基づいて容易に決定し得る。すなわち、ある点で蒸気還元反応器中の水素製造速度が、蒸気還元を停止して酸化金属から金属の再生を開始するのが経済的に有利である点まで低下するであろう。
【００６２】
スラグの還元性清浄化と考え得るこの再生工程では、スラグ中の酸化鉄が還元され鉄として溶融物に戻される。これは反応器に還元剤を導入することによって系の酸化能力を低下させることによって達成される。還元剤は系の酸化能力を低下させ、それによって鉄を溶融物の中へ押し戻す。還元剤は一酸化炭素、石炭および／または他の炭素源であることが可能である。好ましい実施形態によれば、系の酸化能力は粒子化した炭素、炭化水素または液体炭化水素を激しく攪拌した条件下で酸素含有ガスと共にスラグ中へ注入することによって低下させる。粒子化した炭素または炭化水素はコークス、石炭または他の有機材料を含むことが可能である。＃６または他のオイルなどの液体炭化水素もまた使用することが可能である。廃タイヤなどの廃棄材料も使用し得る。廃タイヤは、偶発的な鉄の損失を補うために、反応器へ追加の鉄を有利に供給することが可能である。
【００６３】
先端部浸漬ランスは、空気または他の酸素含有ガスを良好な攪拌を確保するようにして反応器中へ導入するのに好ましい。還元組成物を注入する前に、反応器は蒸気などでパージして、反応器から水素を全て除去することが可能である。スラグの還元性浄化が完了した後、反応器は、鉄に溶解し得る炭素の全てを除去するため、および／または蒸気が再び反応器の中へ導入されたときに生成した水素を汚染するであろう、溶融物またはスラグ中のいずれかに存在し得る他の全ての混入元素を除去するために、再び空気または蒸気でパージすることが可能である。
【００６４】
本発明の好ましい実施形態では、石炭などの炭素源から誘導された還元剤、および空気または酸素リッチ空気などの酸素源が溶融金属混合物およびスラグ層中に注入される。石炭は先端部浸漬ランスを通して空気と共に注入、あるいは分離して加えることが可能である。還元剤として石炭を使用することは、石炭がオイルやガスと比べて豊富で比較的安価であるので有利である。また、石炭は加工中に失われた鉄を補うために鉄を供給することが可能である。廃タイヤおよび他の廃棄材料もまたいくらかの鉄を供給することが可能である。酸化金属還元工程は十分な量の金属鉄が溶融金属混合物中に再び溶解するまで継続される。
【００６５】
酸化金属を金属に還元するモードで運転するときの反応条件は、蒸気還元の間の条件と実質的に同一であることが好ましい。すなわち、酸化金属還元反応器の温度と圧力が蒸気還元反応器の温度と圧力に等しいか非常に類似していることが好ましい。したがって、温度は少なくとも液相（例えばスズ／鉄系で約１１３４℃）以上が好ましく、少なくとも約１２００℃以上であることがより好ましい。温度は約１４００℃を超えないことが好ましく、約１３００℃をこえないことがより好ましい。特に好ましい実施形態では、温度は両反応器とも約１２００℃であり、圧力は蒸気還元反応器で大気圧よりも僅かに高く、酸化金属還元反応器で僅かに低い。
【００６６】
図５を参照すれば、酸化金属還元モードで運転する反応器５００が示されている。反応器は図４に示した蒸気還元反応器と物理的に同一であり、断熱側壁５０２を含むことが好ましい。いくらかの鉄もまた存在するであろうが、金属混合物５０４は初期には主としてスズを含む。スラグ層５０６は上述の蒸気還元工程中に生成した酸化鉄を含む。石炭の形などの炭素５１４は、酸素リッチ空気などの酸素源と共に、反応器の上部壁５１２を貫通して配設されたランス５０８を通して注入される。あるいは、炭素は反応器に分離して加えることが可能であり、ガス状酸素源はランスを通して注入することが可能である。炭素および酸素を加えることによって酸化金属還元反応器中に維持された還元条件下で、酸化鉄は鉄に還元され、次いで溶融金属混合物５０４内に再び溶解する。二酸化炭素および窒素などの排ガス５１６は流出口５１０を通って除去可能である。
【００６７】
酸化金属還元工程で、石炭から生成された灰もまたスラグ中に取り込まれる。フラックスとしてＣａＯを加えるとポゾランになり得るスラグは、定期的にまたは連続的に取り出して粉砕し、ポルトランドセメントの代わりにすることが可能である。あるいは、スラグは水で急冷して部分的に顆粒にすることが可能である。顆粒化スラグは次いで排出し廃棄することが可能である。燃焼中にガス状の化学物質（二酸化硫黄、塩化水素、およびフッ化水素など）に変換された石炭中の不純物（例えば硫黄、塩素およびフッ素）は、湿式洗浄によって除去することが可能である。あるいは、硫黄は肥料化合物として有用な硫化アンモニウムに変換することが可能であり、反応して固形物になった残る不純物は廃棄に振り向けることが可能である。空気および燃料からの二酸化炭素および窒素は酸化金属還元工程からの唯一のガス状排出物である。
【００６８】
スラグの酸化能力を制御することによって、鉄に還元され続いて酸化金属還元中に溶融物に伝達されるスラグ中の酸化鉄の量を制御する。これは、スラグ系に注入される石炭（または他の炭素質燃料）および酸素の量の比を制御することによって達成することが可能である。ある酸化鉄は、スラグの化学的性質によって定まる量がスラグに溶解するであろう。酸化鉄の他の部分は、スラグが酸化鉄中に飽和するならば、スラグ中にスラリー状の粒子化した固形物として存在するであろう。
【００６９】
前述のように、水素製造のために２つ以上の反応器を平行に連続的に運転可能であることは明らかである。鉄が蒸気還元反応器中の溶融金属混合物からなくなり、酸化鉄が酸化金属反応器中で金属に還元されると、反応器への流入と流出を切り替えることによってそれらの機能を逆にすることが可能である。反応器の機能を逆にしても、反応器への金属または酸化金属の流出入の動きはない。このことはコストに大きなまた有利な影響を与える。反応器には蒸気を注入し、あるいは炭素と酸素を注入して一酸化炭素を生成する単一の先端部浸漬ランスを用いることが可能である。あるいは、２つのランス（１つは蒸気用、他は炭素／酸素用）を備える反応器を用いることが可能である。蒸気を注入するための追加の流入口を反応器の側部などに提供することも可能である。
【００７０】
本発明による２つの反応器を用いた連続的な水素生成のフローシートが図６に示されている。
水素生成工程は２つの反応器６０２および６０４を使用し、反応器の１つは蒸気還元モードで運転し、他は酸化金属還元モードで運転する。図６に示したように、反応器６０２は蒸気還元モードで運転して水素を生成し、反応器６０４は酸化金属還元モードで運転している。
【００７１】
蒸気は廃熱ボイラー６０６および６１０で水を加熱して提供される。ボイラーで加熱する前に、水は逆浸透膜および脱イオンなどを用いることによって浄化６１２を行い、ボイラーの運転に影響を与え、あるいは水素ガス生成物に不純物を導入する可能性のある汚染物質を除去しなければならない。蒸気はボイラー中で製造され、蒸気還元反応器６０２の内部を運転温度、例えば約１２００℃で等温条件に維持するのに十分な過熱温度で反応器６０２に提供される。
【００７２】
蒸気は先端部浸漬ランス６０８を通して反応器６０２に注入される。先端部浸漬ランスは良好な攪拌、および蒸気と溶融金属混合物間の高い接触面積を提供し、蒸気還元／金属酸化反応を促進する。反応器６０２は水素および蒸気が反応器から漏出するのを防ぐために密閉されている。また、蒸気に十分な接触時間を提供し、水素を圧力下で送達するように反応器は適度な圧力下に置くことが可能である。
【００７３】
必要であれば他の材料を反応器に加えることが可能である。例えば、蒸気還元反応が金属を酸化するとき溶融金属混合物の上に生成されるスラグ層の特性を制御するために、フラックス６１４を加えることが可能である。可能なフラックスには、ＳｉＯ₂、ＦｅＯ、ＣａＯ、ＭｇＯ、Ｎａ₂ＯまたはＫ₂Ｏが含まれる。加えて、スズ化合物、錫鉱石などの他の材料、または鉄化合物または鉱石などの他の材料を、金属価の損失を補うために加えてもよい。特に好ましい実施形態では、錫鉱石（ＳｎＯ₂）がスズの損失を補うために反応器に注入される。
【００７４】
水素と過剰蒸気を含む水素含有ガスは反応器６０２から除去される。水素含有ガスは廃熱ボイラー６０６を通過して追加の蒸気のために熱を提供することが可能であり、それによって熱の価値を節約する。また、水素含有ガス流ガスは、酸化スズの亜酸化物（ＳｎＯ）、スズの水和亜酸化物（ＳｎＯ₂Ｈ₂）、および溶融金属浴およびスラグから揮発し、あるいは排出されて混入した（凍結）スラグの粒子など、いくらかの汚染物質を含む可能性があり、その汚染物質はバグハウス６１６で除去することが可能である。例えば、揮発性スズ化合物はガス流から凝縮させ、粒子化スラグと共に廃熱ボイラーまたはバグハウスの中で捕捉させることが可能である。捕捉の後これらの材料はペレット化６１８し、場合によっては、金属価の回復およびスラグの化学的性質の制御のために、蒸気還元モードで運転している反応器６０２、または酸化金属還元モードで運転している反応器６０４のいずれかに提供することが可能である。汚染物質を除去した後、場合によっては、水素ガス流を凝縮器６２０および／または冷却器（図示せず）中で処理して水素ガス流からの過剰の蒸気を凝縮し、高純度の水素ガス流６２２を生成する。水素ガス流から凝縮した水は追加の蒸気製造のために再循環させることが可能である。
【００７５】
同時に、酸化金属は反応器６０４の中で還元される。酸化金属は、石炭６２４（または他の炭素質材料）と酸素６２６を先端部浸漬ランス６２８を通して注入することによって生成することの可能な、ＣＯなどの還元剤で還元される。反応器６０２に関しては、先端部浸漬ランス６２８が反応物間の良好な攪拌と接触表面積を提供する。また、水素含有ガスも先端部浸漬ランスまたは同様な装置を用いて注入しなければならない。粒子状石炭は単純に石炭を反応器に投入するなど、他の手段で反応器６０４に加えることが可能である。
【００７６】
反応性酸化金属の還元を行うために酸素と共に使用される、一般に石炭（または他の炭素質材料）の一部である灰を形成する鉱物は、反応器６０４中のスラグ層に貢献する。石炭６２４を使用し、スラグ中に十分な酸化カルシウム（ＣａＯ）があれば、スラグ層は商品性のあるポゾラン副生産物となり得る。反応器６０２に関しては、フラックスなどの他の材料を反応器６０４に注入して、例えばスラグの流動性または発泡性などのスラグの特性を制御することが可能である。
【００７７】
酸化金属還元反応器６０４からの排ガスは二酸化炭素、窒素、および硫黄など石炭からのいくらかの汚染物質を含む可能性がある。排ガスからの熱は蒸気を発生する廃熱ボイラー６１０で保存される。ガス流は次いでバグハウス６３０中で処理し、粒子化汚染物質を除去することが可能である。残るガスは石灰石スクラバー６３２中で処理し、環境に優しい煙道ガスおよび石炭から生じる硫黄からの石膏を生成することが可能である。あるいは、硫黄は無水アンモニアで処理して、土壌の肥料として有用な化合物、硫化アンモニウムを生成することが可能である。
【００７８】
このようにして、鉄が蒸気還元反応器６０２中の溶融金属混合物からなくなり、酸化鉄が酸化金属還元反応器６０４中で鉄に還元されると、反応器への流出入を切り替えることによってそれらの機能を逆にすることが可能である。ガス流を切り替える前に、場合によっては、反応器はパージして残留ガスおよび汚染物質を除去することが可能である。したがって、水素ガスは実質的に連続的に製造することが可能である。
【００７９】
本発明によって製造される水素ガスは高純度であることが好ましい。ガス流は、主として蒸気の形の水からなる残留化合物の少なくとも約３０容量％の水素を含むことが好ましい。水素の純度は、凝縮器で残留水を除去した後に、９９％以上が好ましく、９９．９％がより好ましい。水素ガスが、メタンの蒸気改質または石炭のガス化のいずれか、現在製造されている水素の大部分を占める２つの方法のいずれかによって製造した水素の場合のように、一酸化炭素および二酸化炭素など他のガス状化学物質から分離する必要がないことは本発明の利点である。溶融混合物中に溶解した炭素のために、炭素物質（例えばＣＯ）が当初からガス流の中に存在する場合には、ガスを採収し、水素の純度が十分なレベルに達するまで燃料価のために燃焼することが可能である。すなわち、すべての溶解した炭素は、大量の水素が反応性金属の酸化によって製造される前に、蒸気と優先的に反応してＣＯを生成する。さらに、本発明の方法および装置は、低コストで大量の純粋な水素ガスの製造を可能にする。水素ガスは、約５１，６２３ＢＴＵ／ｌｂ（１３，００９キロカロリー）の燃料価を有し、燃焼ガスの成分として有用である。また、水素は水素化工程および半導体製造に使用することが可能である。さらに、プロトン交換膜燃料電池（ＰＥＭＦＣ）などの燃料電池の燃料として直接使用することができる。
【００８０】
本発明の一態様は、一般にエネルギー変換に伴う石炭の有害な副生産物を大気に排出することを最小にしながら、石炭からエネルギー価を生産する石炭の処理を目的とする。方法は、有害な副生産物を大気へ放出することを最小にしつつ、石炭から中間ＢＴＵガスの形で利用可能な含有エネルギーを抽出することを可能にする。
【００８１】
石炭は合衆国、およびエネルギー生産基幹施設が開発途上の第三国を含む多くの他の地域に比較的豊富に存在する。石炭の使用に伴う問題の１つは、石炭が一般に硫黄を含み、その鉱物質含有物を清浄化しまたは除去しなければならならず、それにも拘らず、通常、環境基準に合致させるために燃焼後ガスの洗浄が追加として必要なことである。
【００８２】
石炭原料が高硫黄石炭を含む低級の石炭、および他の低級石炭を含む可能性のあることは、本発明の利点の１つである。それらの低級石炭は容易に入手可能であり、低コストで入手可能である。本明細書に用いている用語「低級石炭」は、２重量％を超える硫黄含有量、および約１０重量％を超える灰含有量を有する石炭を指す。
【００８３】
一般に、本発明の方法は、石炭原料を水素化ユニットに提供し、石炭原料を前述のようにして製造したＨ₂を含む処理ガスに接触させることを含む。揮発性のある石炭中の炭化水素は水素と反応してメタン（ＣＨ₄）を生成する。水素化ユニットからの排出ガスは、必要であれば洗浄して、清浄な高ＢＴＵガス生成物を製造することが可能である。このガス生成物の一部は、発生器の高い熱−電気変換効率を利用して、複合サイクル発電機中で燃やすことが可能である。ガス生成物の他の部分は、水素化ユニット中に生成した不揮発性炭素と共に従来のボイラーで燃焼させることが可能である。水素処理ガスは強い脱硫黄剤であるので、炭素は実質的に硫黄を含まない。一実施形態では、水素化ユニットで製造された炭素の他の部分は、酸化金属還元工程に循環して戻すことが可能であり、酸化金属は反応性金属に還元される。このようにして石炭は揮発物（水素で処理された）および固定炭素（酸素と反応した）へ有利に分離される。
【００８４】
図７を参照すれば、石炭７０２は、場合によって他の有機物と共に、最初に石炭の温度を上昇させる予備加熱器７０４へ運ばれる。加熱された石炭は次いで水素化ユニット７０６に運ばれ、石炭は上述した方法によって生成した水素ガス７０５と接触する。
【００８５】
水素化ユニット７０６は、流動床反応器または粒子状石炭の処理に適した他の反応器であり得る。ユニットは約５ｐｓｉ（３５１ｇ／ｃｍ²）以下の圧力など、大気圧または大気圧に近い圧力で運転することが好ましい。
【００８６】
水素化ユニット７０６がかなり高い圧力で運転されないことは本発明のコスト上の利点である。著しく高い圧力は、非常に高いＢＴＵを含有するガスである、追加のメタンを生成する。しかし、石炭を清浄なエネルギーに変換するためには、水素化工程の残留物であるコークスから、可燃焼ガスの一酸化炭素および水素を製造することがよりコスト効率がよい。コークスと蒸気（ＣＯおよびＨ₂）間の反応から誘導されたガスは、水素化からのメタンと結合して価値のある中間ＢＴＵガスを生成する。水素化ユニット７０６中の反応は、少なくとも約７００℃で実施することが好ましく、約８００℃〜約９００℃など、約１１００℃を超えないことが好ましい。水素化ユニット中で起きる反応は発熱反応であり、外部熱を追加する必要は極小である。
【００８７】
石炭は主として有機化合物である化学化合物の複雑な混合物である。石炭は大部分が炭化水素であるが、硫黄および窒素などの不純物が石炭には捕捉されている。石炭が燃焼すると放出されるこれらの不純物は、大気に放出されると硫酸および硝酸を生成し、一般の石炭ベースの発電所では排ガスから洗浄されねばならない。さらに、石炭が燃えるとき、炭素が大気中の酸素と結合してＣＯ₂、すなわち地球の熱を捕捉する良く知られたグリーンハウスガスを生成する。
【００８８】
本発明によれば、石炭７０２を水素化ユニット７０６中で水素処理ガス７０５で処理するとき、石炭は燃えない。むしろ石炭中の揮発成分を除去するために加熱される。これらの揮発成分は、大部分メタンからなる高ＢＴＵ製品ガスを有利に生成する。揮発分を除去した残りは水素の作用で浄化され、その浄化には硫黄および窒素の除去が含まれる。得られる浄化された炭素（例えばコークス７０７）は、（ａ）有害な過剰の副生産物を生成することなく従来のボイラー中でメタンと共に燃焼する、（ｂ）一酸化炭素と水素に変換されて、そのガスは水素化反応器７０６からのメタンに加えられて中間の燃焼用ＢＴＵガスを生成する、（ｃ）酸素と蒸気によって活性化された活性炭７１６を生成する、または（ｄ）これらの組み合わせを行う。
【００８９】
水素化反応から製造されたメタン含有ガス流は廃熱ボイラー７０８を通してガス流からの熱価を保存することが可能である。その後、石灰石、生石灰またはアンモニアスクラバーを用いてメタン含有ガス流から硫黄などの汚染物質を除去し、それによって高純度のメタン含有ガス７１２を製造することが可能である。石炭中の硫黄は硫化水素（Ｈ₂Ｓ）を生成するであろうが、これはメタンガス流から洗浄することが可能である。場合によっては、燃焼が大量のガス流を発生するので、燃焼前にメタンガス流を洗浄することが有利である。
【００９０】
メタンガスは電気を発生するために現場で燃焼することが可能であり、またはＣＯ（もしあれば）を除去してパイプラインガスとして最終使用者へ供給することが可能である。さらにＣＨ₄の一部は、他のユニット運転へ循環して戻し、加工熱を提供することが可能である。例えば、ＣＨ₄の一部は、蒸気過熱ヒータ７１４へ迂回させることが可能である。
【００９１】
水素化処理は有利に石炭７０２中の不純物を除去し、清浄なコークス生成物７０７を生成する。コークス生成物７０７は、必要ならば活性化／酸化ユニット７１８中で処理することが可能であり、（ａ）活性化された清浄な炭素７１６、（ｂ）清浄なコークス、（ｃ）水素と一酸化炭素からなる混合ガス、または（ｄ）前述のいくつかの組み合わせを生成する。
【００９２】
本発明の一実施形態によれば、コークス７０７の一部は、酸化金属を還元するために酸化金属還元反応器（図５）に循環して戻すことが可能である。炭素はＣＯおよびスラグに取り込まれた灰に変換され、これは定期的に取り除くことが可能である。水素化ユニット７０６からの残るコークスは従来のボイラー中で追加のエネルギー製造のためにメタンと共に燃焼させることが可能である。
【００９３】
さらに、蒸気の還元によって製造される水素ガス７０５の一部は、水素化ユニット７０６から迂回させ、単独でまたはメタンガスと組み合わせて直接燃料源として使用することが可能である。例えば、水素は、ボイラー、内燃機関、または燃料電池の中で直接燃やすことが可能である。
【００９４】
上述のように、本発明の水素化ユニットへの主要な原料は高級石炭と同様、低級石炭であることが可能である。実際、低級石炭原料はそれらが一般に低コストで入手可能であるので有利である。一実施形態では、少なくとも１重量％の硫黄を有する低級石炭であることが好ましく、少なくとも２重量％の硫黄はさらに好ましい。石炭は粉砕して水分を除去するなどの処理を行うことが可能である。例えば、石炭を粉砕して最大粒子サイズが約１ｍｍを超えないように小さくすることが望ましい。原料が粉砕した石炭であると、水素化工程では高純度で細かく分かれた炭素生成物が得られる。
【００９５】
本発明の水素化処理によって石炭中の揮発物（例えば炭化水素）はメタンに変換される。揮発物質の少なくとも約９０重量％がメタンに変換されることが好ましく、少なくとも約９５重量％がより好ましく、少なくとも約９９重量％がさらにより好ましい。
【００９６】
上述したように、石炭は多くの場合高いレベルの硫黄を含む汚染物質を含む。本発明の方法は、残留コークスと同様石炭の揮発物質部から、有利に、また直ちに汚染物質を取り去る。例えば、硫黄は水素ガスと反応して硫化水素を生成し、これは廃棄流から容易に除去することが可能である。
【００９７】
さらに、本発明の方法は、石炭原料からエネルギーを作り出すことを可能にし、同時に、生成したエネルギーのキロワット−時当たり、一般に従来の石炭燃焼発電所で生成されるよりも極めて少ない二酸化炭素を生成する。発生した電力キロワット−時に対するこの低い二酸化炭素の比率は、本発明の方法が固形燃料の石炭を中間ＢＴＵのガス状燃料に変換するので、自然に生じるものである。固体燃料の熱電変換効率（％で表される）は、２０代半ばから３０代前半の範囲であるが、一方ガス状燃料では熱電変換は５５〜６０％である。二酸化炭素放出における還元は重要な環境上の要素であり、方法にさらに価値を与える。
【００９８】
上述したように、水素化ユニットで製造された炭素は活性炭である。活性炭は多くのガス、蒸気およびコロイド状固形物の高い吸着を特徴とする非晶質の形をしている。活性炭の内部表面積は数百ｍ²／グラムを超え、密度は約０．８５ｇ／ｃｍ³を超えない。活性炭には高い価値があり、空気および水の浄化、廃棄物処理、煙道ガスからの水銀（Ｈｇ）およびＳＯ_xの除去に使用することが可能である。したがって、水素化工程は石炭に適用すると、価値のある副生産物と同様に高ＢＴＵ価のガス流を提供する。
【００９９】
石炭に加えて、他の炭化水素含有原料も同様に処理を行ってメタン（ＣＨ₄）を含む価値のあるガス生成物を製造することが可能である。原料は水素化ユニットに供給され、そこで原料の一部がＣＨ₄に変換するように、Ｈ₂を含む大量のガス組成物と高温で接触する。
【０１００】
本発明の１つの利点は、原料が非常に低コスト、または負の総コストで入手可能なものを含む事実上任意の炭化水素含有原料であり得ることである。
【０１０１】
一実施形態では原料は自治体の廃棄物である。自治体の廃棄物には、一般家庭および産業廃棄物、有害な廃棄物、動物廃棄物、下水汚泥、自動車の細切廃棄物（ＡＳＲ）、ゴムタイヤの破片、および同等品を含み得る。自治体の廃棄物は、自治体が廃棄物の撤去および破壊のために「心付け」料金を支払うので、通常負の総コストで入手可能である。
【０１０２】
合衆国環境保護局によれば、合衆国は１９９８年に２．２億トンの自治体廃棄物を発生した。１人当たりの廃棄量は１９６０年の１人１日当たり２．７ポンド（１．２２６キログラム）から１９８０年の１人１日当たり３．７ポンド（１．６８０キログラム）、１９９８年の１人１日当たり４．５ポンド（約２．４０３キログラム）へと着実に増加してきた。１９９８年のＥＰＡによる合衆国の自治体廃棄物の成分（再生前）は表３に示されている。
【０１０３】
【表３】

【０１０４】
原料が自治体の廃棄物である場合、必要であれば原料を処理し分別することが可能である。例えば、鉄および鋼などの磁性金属は容易に取り除きスクラップとして売却可能である。場合によっては、セルロースベースの材料（例えば紙および木材）も原料中の酸素化合物のレベルを下げるために原料から除去することが可能である。例えば、紙および厚紙、庭の刈り込み屑および木材を含む、この軽く比較的乾燥した廃棄物部を分別するのに、例えば空気分別を使用することが可能である。食物廃棄物、プラスチック、ゴム、皮革、非鉄金属、およびガラスを含む、残る廃棄物は水式分類によって分別することが可能である。非鉄金属およびガラスは別の場所で再生することが可能である。
【０１０５】
上述したように、用語「自治体の固形廃棄物」は居住者および一般産業廃棄物だけではなく、自動車の細切廃棄物（ＡＳＲ）や「綿ほこり（fluff）」を含み得る。主として非鉄金属成分である再生自動車のＡＳＲは、プラスチック、ゴム、繊維、未回収金属および泥の不均一な混合物である。ＡＳＲのプラスチック含有量は一般に約２０重量％であり、自動車製造に使用されるプラスチックの量が増加するに伴って増加している。ＡＳＲは現在地上を埋め、ある地域ではＡＳＲを廃棄コストが劇的に増加している有害廃棄物として法の制定が提案されている。したがって、ＡＳＲを有用な製品ガスに変換することは大きな環境および環境保護の救済となるであろう。
【０１０６】
石炭同様、自治体廃棄物は熱を使用して揮発物と固定炭素に分別し得る。自治体廃棄物からの揮発物の化学組成物は総称ＣＨ_xで表すことが可能である。すなわち、廃棄物が水素化ユニット中で大量の水素ガスと接触するときに起きる反応は次のように記述することが可能である。
０．５（４−ｘ）Ｈ₂＋ＣＨｘ→ＣＨ₄ （９）
【０１０７】
大量の可燃性ガスが廃棄物および本発明の方法によって製造されるのが有利である。１トンの自治体廃棄物から約１９，９００，０００ＢＴＵ（５，０１４，８００キロカロリー）を含む約４８，５５０立方フィート（１，３７４立方メートル）のガスを発生させることが可能である。ガスは約８２％の一酸化炭素、１６％のメタンおよび２％の水素からなり、１立方フィート当たり約４１０ＢＴＵ（１立方メートル当たり約３，６９０キロカロリー）を含む。
【０１０８】
他の実施形態によれば、原料は原油、タールサンドまたは類似物質などを含有する炭化水素含有物質であることが可能である。原油は燃料として使用するために地球の地殻から採収した液体炭化水素と種々の石油産出物の混合物である。原油は広範囲に変化する成分および割合の混合物であるので、物理特性は広範囲に変化し、多くの原油はオイル中に汚染物質を含むため価値が低い。本発明はその低級原油を有利に処理して有用なガス生成物を製造することを可能にする。
【０１０９】
タールサンドは瀝青砂とも呼ばれ、高粘度の瀝青で飽和された粗い砂または部分的に固化した砂岩の堆積物である。タールサンドから回収したオイルは一般に合成原油と呼ばれ、潜在的に大部分化石燃料の形をしている。しかし、タールサンドからのオイルの回収は困難でコストがかかる。本発明は低い価値しかないタールサンドから有用なガス生成物を製造することを可能にする。
【０１１０】
また、２つ以上の上述の成分を組み合わせて原料として使用し得ることも認識されよう。例えば、分別した自治体廃棄物の流れに微粉化した石炭を補足することが可能である。
【０１１１】
本発明のさらに他の態様は、反応物として水素ガスおよび窒素ガスを使用するアンモニアの製造を目的とする。本発明の方法の重要な態様の１つは、比較的低コストで大量の水素ガスをインシトゥーに製造することである。アンモニアを製造するための、従来技術に開示された方法の主な障害の１つは、大量の水素ガスおよび水素ガスに伴う高いコストを要することであると考えられている。本発明によれば、大量の水素ガスがin situにおいて経済的に生成される。
【０１１２】
本発明によれば、窒素および水素は、アンモニア（ＮＨ₃）の製造を最大にするためにＨ₂：Ｎ₂のモル比が約３：１で結合される。一般のアンモニア製造方法では、水素と窒素を含むガスは約２００気圧の圧力に圧縮し、約３８０℃〜約４５０℃の温度で鉄触媒の上を通過させる。
【０１１３】
前述の水素および窒素ガスの製造方法を組み込んだアンモニアを製造する方法は図８に示されている。水素を製造するためには、水８０１がボイラー８０２に提供され、蒸気が反応器８１０または８１２の１つに提供される。次に水素ガスは凝縮器８２０を通過して水が除去され、次いでアンモニア合成ループ８４８へ供給される。
【０１１４】
同時に空気８００を酸化反応器８１１に供給して空気から酸素を取り除き、窒素ガス流８２５が提供される。図６に図示した実施形態では、反応器８１１は金属酸化反応器であり、一方反応器８１３は酸化金属還元反応器である。単一の反応器が還元ガスを水素製造および窒素製造ユニット運転の両方に提供するのに有利に使用し得る。
【０１１５】
このようにして水素ガス８２４および窒素ガス８２５がアンモニア合成ループ８４８に提供される。アンモニア合成ループは約２００気圧に及ぶ高圧で運転することが好ましい。加えて、アンモニア合成ループ８４８は高温で運転され、触媒を含むことが可能である。水素および窒素からのアンモニア製造は、マッキャロル（McCarroll）らの米国特許第４，６００，５７１号（特許文献１５）、ピント（Pinto）らの米国特許第４，２９８，５８８号（特許文献１６）、ゲインズ（Gaines）らの米国特許第４，０８８，７４０号（特許文献１７）に示されている。前述の米国特許のいずれもその全体を本願明細書に援用している。
【０１１６】
得られるアンモニアは多くの用途に使用することが可能である。例えば、アンモニアは肥料に使用する尿素へ変換し得る。また、アンモニアは石炭燃焼発電所からのＮＯ_x放出を還元するのに使用し、種々のアンモニア含有化合物の製造に使用し得る。
【０１１７】
本発明の種々の実施形態を詳細に述べてきたが、当業者が修正ならびに翻案をなし得ることは明らかである。しかし、その修正および翻案が本発明の精神と範囲の範疇内にあることを特に理解すべきである。
【図面の簡単な説明】
【０１１８】
【図１】本発明の有用なスズ−鉄金属混合物の二成分系の相図。
【図２】本発明の一実施形態による鉄の含有量の関数として水素の生成速度を示す図。
【図３】本発明の一実施形態による鉄の含有量および反応温度の関数として水素の生成速度を示す図。
【図４】本発明の一実施形態による蒸気還元モードで運転している反応器を示す図。
【図５】本発明の一実施形態による酸化金属還元モードで運転している反応器を示す図。
【図６】本発明の連続水素製造工程フロー図。
【図７】本発明の石炭または他の有機物含有原料処理工程フロー図。
【図８】本発明のアンモニア製造工程フロー図。【Technical field】
[0001]
The present invention is directed to a method for producing hydrogen gas. More specifically, the present invention is directed to a method for producing hydrogen gas by steam reduction in which a vapor is contacted with a molten metal to produce a metal oxide and a hydrogen-containing gas stream. The metal oxide can then be reduced to metal to produce further hydrogen gas. Hydrogen gas may be used for energy generation or various chemical processes such as coal processing and ammonia production.
[Background Art]
[0002]
Hydrogen (H _Two ) Are valuable necessities and special chemicals essential to many industrial processes, including ammonia production and oil refining. In addition, hydrogen can be converted to electricity in fuel cells with efficiencies approaching 80%. In fuel cell conversion, water is all of the by-product and there are no harmful emissions. For these reasons, hydrogen is widely considered to be a future fuel.
[0003]
It is known that hydrogen gas can be produced from many different sources, such as natural gas, biomass, or water, using different technologies such as reforming, gasification or electrolysis. The most common methods are methane steam reforming (SMR), coal gasification, steam reduction, biomass gasification, pyrolysis, and electrolysis.
[0004]
Methane steam reforming is considered to be the most economical and commercially viable method currently available. In the SMR process, methane (CH _Four ) With steam (H _Two O) to produce a gas stream comprising hydrogen and carbon monoxide (CO). The feedstock is generally natural gas, and the cost of natural gas accounts for a large portion of the total production cost.
[0005]
The SMR technique involves at least two major difficulties. One difficulty is that the cost of producing hydrogen depends on the price of natural gas. Natural gas prices are very volatile due to supply / demand issues, which are expected to continue in the future. Second, the hydrogen produced by SMR contains a large amount of carbon oxides that can only be partially removed by costly scrubbing and pressure swing adsorption. The carbon oxides remaining in the SMR hydrogen are converted to ammonia (NH) from the catalyst and hydrogen used in the fuel cell. _Three ) Harmful to manufacturing.
[0006]
Hydrogen production by coal gasification is another commercially established technology, but is only commercially competitive if natural gas is not extremely expensive. In the coal gasification method, steam and oxygen (O _Two ) Is used for gasification of coal producing hydrogen-containing gas. The synthesis gas from the water-gas shift reaction is then converted to carbon dioxide (CO 2) by subsequent pressure swing adsorption or washing. _Two ) Enables high-purity hydrogen to be extracted. In addition, impurities such as acid gas must be separated from hydrogen. Hydrogen can also be produced by gasification of other hydrocarbons, such as residual oil.
[0007]
Steam reduction uses the oxidation of metals that removes oxygen from steam (ie, steam reduces), thereby producing hydrogen gas. This reaction is shown in equation 1.
xMe + yH _Two O → Me _x O _y + YH _Two (1)
[0008]
To complete the cycle in a two-stage steam reduction process, the metal oxide must be reduced to metal using a reducing agent. For example, carbon monoxide (CO) has an oxygen affinity similar to that of hydrogen, which is equal to each other at about 812 ° C. At temperatures above about 812 ° C., CO has a greater affinity for oxygen than hydrogen. Thus, if CO at equilibrium has an oxygen affinity that is greater than the oxygen affinity of the metal, the CO will reduce the oxide of Formula 1 to the metal.
Me _x O _y + YCO → xMe + yCO _Two (2)
[0009]
As is generally said, the function of the metal / metal oxide pair is to convert oxygen from the vapor into a reducing gas ( CO). Metals and metal oxides are not consumed throughout the process.
[0010]
Oxygen partial pressure (pO _Two ) Relates to the ease with which the metal is oxidized (eg, by steam) and the oxide is reduced (eg, by CO). The mathematical notation is pH _Two O / pH _Two Which is proportional to the partial pressure of oxygen. Also, the inverse function quantity equivalent to this is the fraction of hydrogen,
pH _Two / (PH _Two + PH _Two O) (3)
It is represented as
[0011]
Some metals react violently with water to release hydrogen. Examples of the metal include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), and calcium (Ca). ), Strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), silicon (Si), phosphorus (P), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn) ), Yttrium (Y), zirconium (Zr), niobium (Nb), lanthanum (La), hafnium (Hf), tantalum (Ta), and gallium (Ga). At equilibrium, the sum of the oxygen partial pressures of these metals and metal oxides is very low. Once oxides are formed, they are not efficiently reduced to metal by carbon monoxide. Conversely, there are other groups of metals that react with water and generate little hydrogen. These metals include nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), rhenium (Re), and osmium (Os). , Iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lead (Pb), bismuth (Bi), selenium (Se), and tellurium (Te). At equilibrium, the sum of the oxygen partial pressures of these metals and metal oxides is very high. Therefore, oxides can be easily reduced by carbon monoxide.
[0012]
Between the aforementioned two metal groups are other metals characterized by an oxygen affinity that is approximately the same as the oxygen affinity of hydrogen. Metals in this intermediate group include germanium (Ge), iron (Fe), zinc (Zn), tungsten (W), molybdenum (Mo), indium (In), tin (Sn), cobalt (Co) and antimony ( Sb) is included. These are elements that can easily generate hydrogen from steam and reduce the resulting oxide with carbon monoxide. That is, these metals have a pH _Two O / pH _Two Is sufficiently low to have an oxygen affinity such that the production of hydrogen can be carried out, and the metal oxide is easily reduced by carbon at the temperatures of conventional pyrometallurgy (eg, about 1200 ° C.). These metals are referred to herein as reactive metals, which means that both the metal can be oxidized by steam and the metal oxide can be reduced by carbon monoxide. .
[0013]
Steam reduction / iron oxidation processes were the major industrial methods of hydrogen production during the nineteenth and early twentieth centuries. At high temperatures, iron deprives water of oxygen and releases pure hydrogen.
3Fe + 4H _Two O → Fe _Three O _Four + 4H _Two (4)
To produce maximum hydrogen from a given amount of iron requires an excess of water. After the production of hydrogen, the water is condensed to release an unpolluted hydrogen gas stream. The reaction products of the steam reduction / iron oxidation method are pure hydrogen and wustite (FeO) and / or magnetite (Fe _Three O _Four ). To regenerate metal, carbon monoxide or carbon captures oxygen from iron oxide, and the metal iron and carbon monoxide or carbon dioxide (CO2 _Two ) Is generated.
[0014]
In early hydrogen production techniques, these two steps were performed at different locations. The main cost components of hydrogen production by this method are the cost of iron used minus the value obtained with the iron oxide produced, and the cost of producing excess steam needed to cause the reaction (temperature Function). This cost has been reduced by the benefits derived from the excess energy recovered from the steam. There are many examples in the prior art of the above method.
[0015]
Abott U.S. Pat. No. 1,345,905 discloses the production of hydrogen from steam by oxidation of iron using multiple reactors. In a four reactor configuration, one reactor is used for iron oxidation (hydrogen production), two are used for iron oxide reduction, and the fourth is used to preheat the reactants. used. The gas stream can be switched between reactors for continuous hydrogen production.
[0016]
U.S. Pat. No. 4,343,624 to Belke et al. Discloses a three-stage method and apparatus for producing hydrogen using the reduction of steam as a hydrogen source. In the first stage, low BTU gas containing oxygen and carbon monoxide is generated from a feedstock such as coal. The low BTU gas then reacts with magnetite in a second stage to produce iron, carbon dioxide, and steam. The iron and steam then react in a third stage to produce hydrogen gas and magnetite. It is possible to return the magnetite to the second stage for the reduction reaction, such as by continuously returning the magnetite to the second stage reactor via the feedstock conduit. At least one of the stages is performed in a rotating fluidized bed reactor.
[0017]
U.S. Pat. No. 4,555,249 to Leas discloses a gas containing reactant powders, such as iron alloy powders, that differ greatly in weight between reduced and oxidized forms. 1 discloses a fractionation unit. The unit includes two zones, an oxidation zone containing the reactant powder and a reduction zone, and hydrogen gas is withdrawn from the oxidation zone. When the reactant powder is converted from the oxidized form to the reduced form, the weight of the powder increases, and the change in weight is used to transfer the reduced powder to the oxidation zone while moving the oxidized powder to the zone. Used.
[0018]
"H" by Straus et al _Two from Biosyngas via Iron reduction and Oxidation "discloses a method for producing hydrogen from biosynthesis gas. _Two And CH _Four H _Two , CO, H _Two O and CO _Two Biosynthesis gas containing is used to reduce magnetite to iron. The iron is then cooled and sent to a hydrogen gas generator where the iron comes in contact with steam and generates hydrogen by steam reduction. The iron oxide is then cooled and returned to the metal oxide reduction reactor for reaction with the biosynthesis gas.
[0019]
The disadvantage of the steam reduction method using iron is that the reaction of solid iron with steam creates an oxide layer that prevents additional steam from reacting with the iron under the oxide layer, thus reducing the reaction rate. It is limited by the rate of gas diffusion through the oxide layer. Also, the reaction rate depends on the surface area of iron available for the reaction. However, a large surface area is equivalent to a small particle size, and processing into small particles is expensive. In addition, there are difficulties associated with the reduction of iron oxide. One method of reducing iron oxide involves the dissolution of oxides, thus resulting in high temperature disadvantages due to the high melting point of iron (1538 ° C.). In another method, iron oxide is reduced to metal in the solid state by carbon and / or a reducing gas. However, this latter method is inefficient and kinetic difficult. Except for solid state reduction, a minimum of 20.8 tons of iron and 28.7 tons of magnetite are physically transferred from one reactor (metal oxidation) to another reactor (metal reduction) per ton of hydrogen produced. Must be moved.
[0020]
Metals other than iron have been used in the steam reduction process. Acker, U.S. Pat. No. 1,050,902, discloses the use of tin or zinc in a steam reduction process to produce hydrogen and the regeneration of metals by reducing metal oxides with coal. Is disclosed.
US Pat. No. 3,821,362 to Spacil discloses Sn / SnO for producing hydrogen. _Two Is used. The molten tin is made fine dust and brought into contact with steam, _Two And hydrogen gas. Then SnO _Two Is produced by contact of coal powder with air, H _Two , N _Two , And CO. SnO _Two Is reduced to liquid tin and then transferred to the first reactor. A similar method for producing hydrogen is shown in U.S. Pat. No. 3,979,505 to Seitzler.
[0021]
Erickson U.S. Pat. Nos. 4,310,503 and 4,216,199 disclose the potential of tin to act as an oxygen carrier from vapor to carbon dioxide. Discloses a comprehensive study. An extension of this work was also reported in Ericsson's "Hydrogen from Coal via Tin Redox," prepared for the US Department of Energy Conservation-Related Inventions in February 1981.
[0022]
Ericsson describes the equilibrium pH of the metal oxidation reaction with steam as the stage in which the yield of hydrogen from a given amount of coal reduction composition is continued. _Two / PH _Two Report that O can be increased by using a multi-step process configured to increase. Among the materials used as intermediates (ie, metal / metal oxide pairs), pure solids are iron, wustite (FeO), tungsten dioxide, molybdenum and germanium, pure liquids are tin and indium, and dissolved Dissolved liquids are tin, indium, germanium, zinc, and iron, where dissolved means that the intermediate is present in less than a unit of activity. The effect of using a dissolved liquid is that the partial pressure of oxygen increases (ie, the partial pressure of hydrogen decreases) and a small amount of hydrogen is produced. Ericsson discloses that a suitable solvent for the dissolved liquid can be selected from one or more inert metals with a high oxygen partial pressure, such as, for example, copper, lead and nickel. It is also disclosed that tin, which is an active metal, can be used as a solvent for indium.
[0023]
When producing hydrogen by using tin in a steam reduction process, the first reaction is:
Sn + 2H _Two O → SnO _Two + 2H _Two (5)
In order to properly ensure the reaction rate of the above reaction, a temperature of about 900 ° C. or higher is required, and tin is a liquid at that temperature (T _m = 232 ° C). Thermodynamics indicate that at such high temperatures a large excess of steam is required to drive the reaction. The need for large amounts of excess steam raises a number of problems. For the process to be economical, heat must be recovered, including the recovery of the heat of evaporation of water to produce steam. Most of this heat recovery is technically possible, but requires additional capital to implement. Also, a large amount of excess vapor must be physically contacted with tin, such as by bubbling liquid tin. In practice, that contact is only possible if the steam and the reactor operate under moderate pressure, and the process of operating at very high pressures is generally very expensive.
[0024]
For example, the production of one ton of hydrogen requires 8.94 tons of steam and 29.4 tons of tin (calculated by stoichiometry). Further, producing 1 ton of hydrogen at 900 ° C. requires 35.7 tonnes of steam to meet thermodynamic requirements. If this total amount of steam required (44.6 tonnes) passes through a stoichiometric amount of tin under atmospheric pressure, the speed of the steam passing through the space not occupied by tin will exceed 100 meters / second. That is, the nominal residence time is less than 1/100 second, and even when the system pressure is increased to 100 atmospheres, only 0.85 seconds is allowed to bring the reaction closer to equilibrium. It is possible to use an excess of tin over the stoichiometrically required amount, and the effect of the higher weight (larger volume) of tin is to increase the nominal residence time. However, due to the increased tin-steam reactor and the required increase in the inventory of tin, this approach to increasing the nominal residence time is expensive.
[Patent Document 1]
U.S. Pat. No. 1,345,905
[Patent Document 2]
U.S. Pat. No. 4,343,624
[Patent Document 3]
U.S. Pat. No. 4,555,249
[Patent Document 4]
U.S. Pat. No. 1,050,902
[Patent Document 5]
U.S. Pat. No. 3,821,362
[Patent Document 6]
U.S. Pat. No. 3,979,505
[Patent Document 7]
U.S. Pat. No. 4,310,503
[Patent Document 8]
U.S. Pat. No. 4,216,199
[Patent Document 9]
U.S. Pat. No. 3,905,807
[Patent Document 10]
U.S. Pat. No. 4,251,271
[Patent Document 11]
U.S. Pat. No. 5,251,879
[Patent Document 12]
U.S. Pat. No. 5,282,881
[Patent Document 13]
U.S. Pat. No. 5,308,043
[Patent Document 14]
US Pat. No. 6,066,771
[Patent Document 15]
U.S. Pat. No. 4,600,571
[Patent Document 16]
U.S. Pat. No. 4,298,588
[Patent Document 17]
U.S. Pat. No. 4,088,740
[Non-patent document 1]
"H2 from Biosyngas via Iron reduction and Oxidation" by Straus et al.
[Non-patent document 2]
Ericsson's "Hydrogen from Coal via Tin Redox" prepared for the US Department of Energy Conservation-related Inventions (February 1981)
[Non-Patent Document 3]
Harikmar K. C. (Hari Kumar, KC, et al.), Calphad, Vol. 20, No. 2, pp. 139-149 (1996)
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
[0025]
Therefore, there remains a need for a method for producing hydrogen that is technically reliable and economically feasible. Both steam / iron and steam / tin processes are technically feasible. But neither is economically feasible. The steam / iron process is unsatisfactory because (1) the production of hydrogen is diffusion controlled, (2) the cost of moving the metal is high, and (3) it is difficult (cost) to reduce iron. The vapor / tin process has poor reaction rate at low temperatures (less than about 800 ° C.) and poor thermodynamics at high temperatures, and thus lacks economic feasibility. Poor thermodynamic results require large volumes of steam to be processed through the molten metal, increasing process difficulties and costs. Despite the high need for hydrogen gas, we do not know of any commercial equipment capable of performing a steam reduction process due to these and other factors.
[Means for Solving the Problems]
[0026]
According to one embodiment of the present invention, a method for producing a hydrogen-containing gas stream is provided. The method includes the steps of generating steam and contacting the steam with a molten metal mixture having at least about 20% by weight of iron dissolved in a diluting metal, wherein at least a portion of the iron is oxidized to a metal oxide. And at least a portion of the steam is reduced to produce a hydrogen-containing gas stream. Preferably, the diluting metal is tin. Contacting the steam with the iron dissolved in the diluent metal reduces the problems associated with the thermodynamic and kinetic constraints inherent in conventional steam reduction processes.
[0027]
According to another embodiment of the present invention, there is provided a method of producing a hydrogen-containing gas, wherein steam is generated and contacted with a molten metal mixture at a temperature of at least 1100 ° C. The molten metal mixture includes a reactive metal dissolved in a diluent metal, where the reactive metal is oxidized and the steam is reduced to produce hydrogen. Using a temperature of at least about 1100 ° C. for the molten metal mixture allows for the production of hydrogen under suitable thermodynamic and kinetic conditions.
[0028]
According to another embodiment, there is provided a method of producing a hydrogen-containing gas stream comprising generating steam and contacting the steam with a molten metal mixture in a reactor, wherein the reactive metal-containing particles are provided. Dispersed in the molten metal mixture. As the reactive metal is oxidized by the vapor, the reactive metal-containing particles advantageously provide additional reactive metal to the molten metal mixture.
[0029]
According to another embodiment, there is provided a method of producing a hydrogen-containing gas stream comprising contacting a vapor with a molten metal mixture in a reactor, the molten metal mixture comprising a reactive metal dissolved in a diluent metal. Including. The reactive metal is oxidized by the steam to a metal oxide. The metal oxide is then reduced in the reactor to a reactive metal.
[0030]
The hydrogen-containing gas stream produced as described above is used in various processes and is particularly suitable for the treatment of carbon-containing substances such as coal or waste, and for the production of chemicals such as ammonia.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031]
According to the present invention, hydrogen gas (H _Two ) Comprises a molten metal mixture comprising at least a first reactive metal at least partially dissolved in at least one diluent metal and water vapor (H _Two O). The diluting metal may be reactive with the vapor, but by definition is less reactive than the reactive metal. Thus, oxygen from the vapor preferentially reacts with the reactive metal to oxidize the reactive metal to a metal oxide and reduce some of the vapor to produce a hydrogen-containing gas stream that also contains excess vapor. In a preferred embodiment, the production of hydrogen continues until the concentration of the dissolved reactive metal in the molten metal mixture is reduced to the lowest concentration determined by economics, at which point the steam injection is terminated. The reducing agent is then introduced into the reactor under vigorous stirring conditions, such as with a tip immersion lance. Under these conditions, the metal oxide is chemically reduced to the reactive metal and redissolves again in the molten metal mixture. By switching the steam and reducing agent streams between two or more reactors, a substantially continuous production of hydrogen is possible. The method of the present invention offers significant advantages over prior art steam reduction methods.
[0032]
To begin the production of hydrogen, a vapor is contacted with a molten metal mixture comprising at least a first reactive metal and at least a first diluent metal. By definition, reactive metals are those that are more reactive with steam than diluent metals. Preferably, the reactive metal has an oxygen affinity similar to that of hydrogen and reacts with the vapor to produce a metal oxide. For example, reactive metals include germanium (Ge), iron (Fe), zinc (Zn), tungsten (W), molybdenum (Mo), indium (In), tin (Sn), cobalt (Co), and antimony (Sb). ). The molten metal mixture can include one or more reactive metals. Preferred reactive metals are (1) those that are soluble in the diluent metal, (2) those that have a very low vapor pressure at the oxidation / reduction temperature, and (3) that react with the vapor to oxidize. / Produces one or more oxides with very low vapor pressure at the reduction temperature. A particularly preferred reactive metal according to the present invention is iron, and according to one embodiment the reactive metal in the molten metal mixture consists essentially of iron.
[0033]
The reactive metal is at least partially dissolved in the second metal or metal mixture. The metal in which the reactive metal is dissolved is referred to herein as the diluent metal. The diluent metal may also be reactive with the vapor, in which case if the diluent metal is less reactive than the reactive metal, it may be selected from the group of reactive metals disclosed above. It is possible. Alternatively, the diluent metal may be an oxygen partial pressure (pO _Two ) Can be selected from relatively high metals. These metals include nickel (Ni), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), rhenium (Re), and osmium (Os). , Iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), lead (Pb), bismuth (Bi), selenium (Se), and tellurium (Te). One or more diluent metals can be used in the molten metal mixture. The diluent metal must not be a metal with a very low oxygen partial pressure at equilibrium of the metal and the metal oxide.
[0034]
Preferred diluent metals are (1) combined with the reactive metal and become liquid in the temperature range of 400 ° C. to 1300 ° C., (2) above this temperature range the vapor pressure is very low and (3) in solution It has the ability to retain reactive metals. According to a preferred embodiment of the present invention, the diluent metal is tin, and in one embodiment, the diluent metal consists essentially of tin. However, the molten metal mixture can also include additional diluent metals, especially copper and nickel.
[0035]
A particularly preferred molten metal mixture for the steam reduction of the present invention comprises iron as the reactive metal and tin as the diluent metal. Iron is highly soluble in molten tin at high temperatures, and the melting temperature of the mixture is much lower than the melting temperature of pure iron (1538 ° C.). Tin is also reactive with steam, but less reactive than iron.
[0036]
For thermodynamic reasons, the steam reduction reaction to produce hydrogen gas requires an excess of steam over the stoichiometrically required amount. The total amount of steam required for iron (the mass ratio of steam required for hydrogen produced) is much less than tin at all temperatures, and iron is preferentially oxidized in the molten metal mixture. That is, although not theoretically supported, it is considered that some reactive tin is oxidized to tin oxide and immediately reduced to tin.
[0037]

[0038]
The thermodynamic steam requirement for tin at 660 ° C. is approximately equal to the thermodynamic steam requirement for iron at 1200 ° C. However, producing hydrogen using tin as a reactive metal at 650 ° C. has very poor kinetics (ie, reaction rate) and therefore very long residence time (ie, the time that steam is in contact with tin). ) Is not practical.
[0039]
At 1200 ° C., the reaction rates of tin and iron are excellent. However, tin has a much higher steam requirement than iron. According to the invention, the residence time during which the vapor contacts the reactive metal is increased by using a diluting metal. For illustration, the thermodynamic steam requirement and nominal residence time of the dissolved iron (50% by weight iron in tin) of an embodiment of the present invention at a temperature of 1200 ° C. and various pressures compared to pure tin The comparison is shown in Tables 1 and 2. Table 1 shows the total amount of steam required to produce one ton of hydrogen at 1200 ° C.
[0040]
[Table 1]

[0041]
Table 2 shows the nominal residence time at a hydrogen production rate of 4.439 tonnes.
[Table 2]

[0042]
From the data in Tables 1 and 2, it is clear that a pure tin system requires more steam to produce hydrogen than a molten iron system according to the present invention. Table 2 also shows that the nominal residence time of tin capable of reacting with steam is significantly shorter than the nominal residence time of iron dissolved in tin capable of reacting with steam. Nominal or apparent residence time is the time that steam (the reactants of the process) can pass through the space occupied by the amount of reactive metal used. In Table 2, the molten volume is the stoichiometrically required amount of metal when the hydrogen production rate is 4.439 ton hydrogen / hour. During this time, hydrogen is ideally thermodynamically pH _Two / PH _Two An amount corresponding to the ratio of O is produced. It is possible to increase the nominal residence time by an amount of reactive metal that is higher than the stoichiometric amount, but the result is an increase in reactor size and cost. Also, increasing the pressure increases the possible reaction time between the steam and the reactive metal, but adds cost.
[0043]
Thus, one important advantage of using the reactive metal dissolved in the diluting metal according to the present invention is that the residence time of the vapor in the reactor with respect to the mass of the reactive metal is increased. That is, a constant mass of iron will occupy the first volume as pure iron, but if iron is present as a 50% by weight mixture with a diluent metal such as tin, the same mass of iron would be about twice its volume. Will be distributed.
[0044]
Figure 1 shows Harikmar K. C. A phase diagram of iron and tin adapted from Calphad, Vol. 20, No. 2, pp. 139-149, 1996 (Non-Patent Document 3) is shown. From FIG. 1 it can be seen that one effect of adding iron (reactive metal) to tin (dilution metal) is to significantly lower the melting temperature of iron. The liquid phase metal mixture drops from 1538 ° C. (pure iron) to about 1134 ° C. with a molten composition of about 48.7% by weight of tin and 51.3% by weight of iron.
[0045]
According to one embodiment, the metal mixture is preferably maintained at a temperature above the liquidus line AC of FIG. 1 (eg, about 1134 ° C.). However, too high a metal-steam reaction temperature adds significant operating costs. In the fully molten iron / tin system shown in FIG. 1, the melt must be maintained at a temperature of the liquid phase of 1134 ° C. or higher, more preferably at least about 1200 ° C. To be reasonably economical, the temperature should not be above about 1500 ° C, and more preferably should not be above about 1400 ° C. A particularly preferred temperature range for the fully molten iron / tin metal mixture is from about 1200C to 1300C. At 1200 ° C., about 50% by weight of iron dissolves in the tin with sufficient superheat and the mixture remains molten upon oxidation of the iron. Also, the reaction between steam and liquid iron dissolved in tin, producing pure hydrogen at 1200 ° C., is very vigorous and the reaction rate is excellent. Furthermore, the thermodynamics of the steam / iron system at 1200 ° C. is relatively good, requiring only about 12.2 tonnes of steam per ton of hydrogen (1.37 moles of steam per mole of hydrogen).
[0046]
According to this embodiment, the metal mixture preferably initially comprises at least about 3% by weight of iron in the molten metal mixture, more preferably at least about 10% by weight of iron, and at least about 20% by weight of iron. Preferably, about 50% by weight of iron is even more preferred. Further, the amount of iron in the molten metal mixture preferably does not exceed about 85% by weight, and more preferably does not exceed about 80% by weight. In a preferred embodiment, the balance of the metal mixture consists essentially of tin. Thus, the amount of tin in the system preferably does not exceed about 97% by weight, more preferably does not exceed about 90% by weight, and even more preferably does not exceed about 80% by weight. Preferably, the molten metal mixture contains at least 15% by weight tin, more preferably at least about 20% by weight tin.
[0047]
Although the present invention requires the presence of a molten metal mixture, in one embodiment, insoluble phases, such as particles, may be dispersed in the molten metal mixture. The combination of the molten metal mixture and the insoluble phase is called a slurry. According to one embodiment, the steam is contacted with a slurry comprising the molten metal mixture and a solid second phase. The solid second phase contains particles containing the reactive metal and provides additional reactive metal to the molten metal mixture. Preferably, the particles are metallic particles (eg, not oxide particles). For example, the slurry can include iron-rich metallic particles in an iron / tin melt saturated with iron. As the steam reduction process proceeds, the dissolved iron is removed from the molten metal mixture by oxidation of the iron, and additional iron from the iron-rich particles dissolves in the molten metal to remove the molten metal portion of the iron-saturated slurry. keep.
[0048]
Referring to the phase diagram of FIG. 1, point A (83.3% Fe at 1134 ° C.), point B (84% Fe at 1134 ° C.), point C (12% Fe at 895 ° C.), and point D (895% The composition in the two-phase region bounded by (3% by weight of Fe at 0 ° C.) comprises an iron / tin melt having a total amount of about 3% to 84% by weight of iron, some of the iron dispersed in the melt. It is a metallic particle rich in iron. As iron is removed from the molten metal by oxidation at a predetermined temperature between about 895 ° C. and about 1134 ° C., additional solid iron from the iron-rich particles dissolves, thereby reducing the level of iron in the melt. Maintain bulk saturation until no solid iron is present. This non-oxidative replacement of iron by the iron resulting from the iron-rich particles keeps the iron activity high, ie, maximizes the production of hydrogen. For example, at a temperature of about 950 ° C. and a total iron amount of about 50% by weight, the molten metal mixture will contain about 4% by weight dissolved iron in the system. As the dissolved iron is oxidized, additional metallic iron from the iron-rich particles dissolves, maintaining the dissolved iron in the melt at 4% by weight. Dissolution of iron-rich particles does not change the activity of iron.
[0049]
Thus, according to this embodiment, the slurry comprising the molten metal mixture and the iron-containing particles is maintained at a liquidus temperature of 1134 ° C or less and at least 895 ° C, more preferably between about 900 ° C and 1134 ° C.
[0050]
One advantage of the method is that the activity of the iron is kept constant, in practice close to 1, so that the rate of hydrogen production is kept constant and maximum throughout the steam reduction process.
The desired effect of the constant activity of the reactive metal will be observed if the process is performed within the miscibility gap region of FIG. 1, but the activity of iron is slightly less than 1. .
[0051]
A thermodynamic relationship exists between the partial pressure of hydrogen in the exhaust gas, the reaction temperature, and the weight percent of iron in the molten metal composition. The thermodynamic amount of iron, called "activity", varies as a function of iron concentration and has a significant effect on the ratio of hydrogen to water in the exhaust gas. Hydrogen production is maximized by operating in a phase region where high iron activity is established over a wide composition range by using a second phase that is in equilibrium with the reaction phase. This applies both to the liquid-liquid phase region above the line AC in FIG. 1 and also to the solid-liquid region below the line AC and to the right of the line AB. However, the invention does not preclude implementation in an iron-rich liquid phase.
[0052]
FIG. 2 shows the relationship between the level of hydrogen in the off-gas as a function of the iron content in the molten metal mixture. FIG. 2 is calculated based on the thermodynamics of the reaction at 1225 ° C. It is clear that as the iron content drops from 20% to 10% by weight, the rate of hydrogen production decreases rapidly. FIG. 3 shows hydrogen production as a function of temperature and iron content.
[0053]
At iron levels below about 20% by weight, and temperatures above about 1134 ° C., hydrogen production capacity decreases. The reason is (1) pH _Two / PH _Two O is greatly reduced, (2) because there is only a short time before switching the gas flow (ie, the vapor and the metal oxide reducing agent).
[0054]
In this way, the steam contacts the molten metal mixture to generate hydrogen and convert the reactive metal to a metal oxide. The steam contacts the molten metal mixture in a manner that promotes good agitation and contact with the molten metal mixture. For example, steam can be brought into contact with the molten metal mixture by injection from a head dip lance or from a porous ceramic diffuser located at the bottom of the reactor. A preferred reactor system in this regard is described below. The temperature of the reactor can be controlled by controlling the temperature and amount of incoming steam and / or by adding oxygen to the reactor and can be maintained at a substantially constant temperature.
[0055]
The steam reduction reactor can be maintained at a high pressure, as described above, if an appropriate residence time in the reactor is required. For example, it may be desirable to maintain at least about 15.3 atmospheres (225 psi, 15503 hectopascals). Slightly increased pressures are also beneficial in providing sufficient pressure for transfer to the hydrogen gas stream (eg, line pressures of about 200 psi (13780 hectopascals). However, very high pressures increase capital costs. To achieve this, the pressure in the steam reduction reactor is preferably no greater than about 600 psi (41341 hectopascals), and more preferably no greater than about 225 psi (15503 hectopascals).
[0056]
According to the invention, a slag layer is maintained on the molten metal mixture. The slag layer offers many advantages, including preventing iron oxide from escaping the reactor. The temperature in the steam reduction reactor must be sufficient to maintain the slag layer formed on the metal mixture in a molten state over a wide range of the composition. When the reactive metal is oxidized, the concentration of the reactive metal in the metal mixture decreases, but the metal mixture must be maintained in a molten state even when the reactive metal is oxidized. Similar to the molten metal composition range described with respect to FIG. 1, the preferred slag composition necessary to ensure sufficient slag fluidity and reactivity, and the prevention of foaming, may be reduced at any given temperature, as required. It is possible to adjust. For example, it is possible to add flux to the reactor to adjust the properties of the slag. One of the flux systems is SiO _Two , FeO, CaO, MgO, Na _Two O and K _Two It can be said that it is a liquid surface of O. However, it is also possible to incorporate sulfur and other cations into this or other slag to ensure sufficient slag chemistry.
[0057]
Metal oxides generated by steam reduction (eg wustite and / or magnetite) can be conveniently captured (dissolved or dispersed) by slag in the reactor. At the preferred temperature, the iron oxide is incorporated into the slag, which is lighter than the metal mixture. Thus, as the dissolved iron disappears from the molten metal mixture, the iron oxide rises through the molten metal and contributes to the slag layer on top of the molten metal. The oxide formed by the reaction of the reactive metal with the steam has a lower density than the density of the molten metal mixture, which causes the oxide to rise into the slag layer. There are two advantages. Preferably, the density of the metal oxide is at least about 10% lower than the molten metal mixture. This also allows the metal to sink from the slag layer into the molten metal mixture as the metal oxide is reduced. As mentioned above, the deposition of iron oxide in the slag can be achieved by maintaining the slag in favorable conditions with respect to viscosity, reactivity, foamability, etc. _Two , FeO, CaO, MgO, Na _Two O, K _Two It will require the addition of a flux such as O or a mixture thereof.
[0058]
The molten metal mixture must be contained in a suitable reactor to maintain the proper reaction conditions. In addition, the reactants must be provided to achieve good agitation and a large contact surface area. Suitable high temperature reactors for establishing good gas / liquid contact are used in the chemistry, and especially in the metallurgy industry.
[0059]
The preferred reactor system of the present invention uses a top-submerged lance to inject steam into the molten metal. The reactor has been used for industrial tin production from tin ore (tinite). Examples of reactors using a tip immersion lance for injecting reactants are described in US Pat. No. 3,905,807 to Floyd et al., US Pat. No. 4,251,271 (US Pat. No. 4,251,271). U.S. Pat. No. 5,251,879, U.S. Pat. No. 5,251,879, Baldock et al., U.S. Pat. No. 5,282,881, U.S. Pat. No. 4,043 (Patent Document 13) and US Pat. No. 6,066,771 (Patent Document 14). Each of these patents is incorporated herein in its entirety. The reactor injects the reactants (eg, steam) at a high velocity near Mach 1 into the molten metal, thereby promoting good stirring of the reactants.
[0060]
A reactor incorporating a lance for injecting steam is shown in FIG. Reactor 400 includes a refractory side wall 402 adapted to receive a molten metal mixture 404. In order to maintain the temperature in the reactor 400, a heating means (not shown) may be provided if necessary. A tip immersion lance 408 is disposed through the top wall 412 to inject steam at a high rate into the metal mixture. The tip immersion lance 408 preferably terminates below the surface of the slag layer 406 and near the interface between the molten metal mixture 404 and the slag layer 406 and injects steam. As steam is introduced through lance 408, iron in metal mixture 404 is oxidized to iron oxide. The iron oxide rises and deposits on the slag layer 406. A gaseous product 416 comprising hydrogen gas mixed with the steam is withdrawn from outlet 410, whereupon excess steam can be condensed to produce a substantially pure hydrogen stream.
[0061]
The steam reduction process is continued until the hydrogen production rate drops to a sufficiently low level. Thereafter, a reducing agent is introduced into the reactor containing the molten metal mixture and the slag to reduce iron oxide to metal. The point at which the steam reduction process is stopped and the service reduction process is started can be easily determined based on economic reasons. That is, at some point, the rate of hydrogen production in the steam reduction reactor will be reduced to the point where it is economically advantageous to stop steam reduction and begin metal regeneration from the metal oxide.
[0062]
In this regeneration step, which can be considered a reductive cleaning of the slag, the iron oxide in the slag is reduced and returned to the melt as iron. This is achieved by reducing the oxidizing capacity of the system by introducing a reducing agent into the reactor. The reducing agent reduces the oxidizing capacity of the system, thereby forcing the iron back into the melt. The reducing agent can be carbon monoxide, coal and / or other carbon sources. According to a preferred embodiment, the oxidizing capacity of the system is reduced by injecting the particulate carbon, hydrocarbon or liquid hydrocarbon under vigorous stirring conditions with the oxygen-containing gas into the slag. Particulate carbon or hydrocarbon can include coke, coal or other organic materials. Liquid hydrocarbons such as # 6 or other oils can also be used. Waste materials such as waste tires may also be used. Waste tires can advantageously supply additional iron to the reactor to compensate for accidental iron loss.
[0063]
A tip immersion lance is preferred for introducing air or other oxygen containing gas into the reactor to ensure good agitation. Prior to injecting the reducing composition, the reactor can be purged, such as with steam, to remove any hydrogen from the reactor. After the reductive cleaning of the slag is completed, the reactor may be used to remove any carbon that may be dissolved in iron and / or contaminate the hydrogen produced when steam is re-introduced into the reactor. It is possible to purge again with air or steam to remove any other contaminants that may be present either in the melt or in the slag.
[0064]
In a preferred embodiment of the invention, a reducing agent derived from a carbon source, such as coal, and an oxygen source, such as air or oxygen-rich air, are injected into the molten metal mixture and slag layer. Coal can be injected with the air through the tip immersion lance or added separately. The use of coal as a reducing agent is advantageous because coal is abundant and relatively inexpensive compared to oil and gas. Coal can also supply iron to make up for iron lost during processing. Waste tires and other waste materials can also provide some iron. The metal oxide reduction step is continued until a sufficient amount of metallic iron is redissolved in the molten metal mixture.
[0065]
The reaction conditions when operating in the mode of reducing metal oxides to metal are preferably substantially the same as those during the steam reduction. That is, it is preferred that the temperature and pressure of the metal oxide reduction reactor be equal or very similar to the temperature and pressure of the steam reduction reactor. Accordingly, the temperature is preferably at least a liquid phase (eg, about 1134 ° C. for a tin / iron system), and more preferably at least about 1200 ° C. Preferably, the temperature does not exceed about 1400 ° C, more preferably it does not exceed about 1300 ° C. In a particularly preferred embodiment, the temperature is about 1200 ° C. in both reactors and the pressure is slightly above atmospheric pressure in the steam reduction reactor and slightly lower in the metal oxide reduction reactor.
[0066]
Referring to FIG. 5, a reactor 500 operating in a metal oxide reduction mode is shown. The reactor is physically the same as the steam reduction reactor shown in FIG. The metal mixture 504 initially contains primarily tin, although some iron may also be present. The slag layer 506 includes iron oxide generated during the above-described steam reduction step. Carbon 514, such as in the form of coal, is injected with a source of oxygen, such as oxygen-rich air, through a lance 508 disposed through the top wall 512 of the reactor. Alternatively, the carbon can be added separately to the reactor and the source of gaseous oxygen can be injected through a lance. Under reducing conditions maintained in the metal oxide reduction reactor by adding carbon and oxygen, the iron oxide is reduced to iron and then redissolved in the molten metal mixture 504. Exhaust gases 516, such as carbon dioxide and nitrogen, can be removed through outlet 510.
[0067]
Ash produced from coal in the metal oxide reduction step is also incorporated into the slag. Slag that can become pozzolans when CaO is added as a flux can be removed and ground periodically or continuously to replace Portland cement. Alternatively, the slag can be quenched with water and partially granulated. The granulated slag can then be discharged and discarded. Impurities (eg, sulfur, chlorine, and fluorine) in the coal that have been converted to gaseous chemicals (such as sulfur dioxide, hydrogen chloride, and hydrogen fluoride) during combustion can be removed by wet scrubbing. Alternatively, the sulfur can be converted to ammonium sulfide, which is useful as a fertilizer compound, and the remaining impurities that have reacted to solids can be directed to waste. Carbon dioxide and nitrogen from air and fuel are the only gaseous emissions from the metal oxide reduction process.
[0068]
By controlling the oxidizing capacity of the slag, the amount of iron oxide in the slag that is reduced to iron and subsequently transferred to the melt during metal oxide reduction is controlled. This can be achieved by controlling the ratio of the amount of coal (or other carbonaceous fuel) and oxygen injected into the slag system. Certain iron oxides will dissolve in the slag in amounts determined by the slag chemistry. Other parts of the iron oxide will be present as a slurried particulate solid in the slag if the slag is saturated in the iron oxide.
[0069]
As mentioned above, it is clear that two or more reactors can be operated continuously in parallel for hydrogen production. Once iron is removed from the molten metal mixture in the steam reduction reactor and iron oxide is reduced to metal in the metal oxide reactor, their functions can be reversed by switching in and out of the reactor. It is possible. There is no movement of metal or metal oxide into or out of the reactor when the function of the reactor is reversed. This has a significant and beneficial effect on cost. It is possible to use a single tip immersion lance that injects steam or injects carbon and oxygen to produce carbon monoxide. Alternatively, a reactor with two lances (one for steam and the other for carbon / oxygen) can be used. Additional inlets for injecting steam may be provided, such as on the sides of the reactor.
[0070]
A flow sheet for continuous hydrogen production using two reactors according to the present invention is shown in FIG.
The hydrogen production process uses two reactors 602 and 604, one of which operates in a vapor reduction mode and the other in a metal oxide reduction mode. As shown in FIG. 6, reactor 602 operates in a vapor reduction mode to produce hydrogen, and reactor 604 operates in a metal oxide reduction mode.
[0071]
Steam is provided by heating water in waste heat boilers 606 and 610. Before heating in the boiler, the water is purified 612 by using a reverse osmosis membrane and deionization to remove contaminants that may affect the operation of the boiler or introduce impurities into the hydrogen gas product. Must be removed. Steam is produced in the boiler and provided to the reactor 602 at a superheat temperature sufficient to maintain the interior of the steam reduction reactor 602 at an operating temperature, eg, about 1200 ° C., at isothermal conditions.
[0072]
Steam is injected into reactor 602 through tip immersion lance 608. The tip dip lance provides good agitation and a high contact area between the vapor and the molten metal mixture and promotes the vapor reduction / metal oxidation reaction. Reactor 602 is sealed to prevent hydrogen and vapor from leaking out of the reactor. Also, the reactor can be placed under moderate pressure to provide sufficient contact time with the vapor and deliver hydrogen under pressure.
[0073]
Other materials can be added to the reactor if needed. For example, a flux 614 can be added to control the properties of the slag layer created above the molten metal mixture when the vapor reduction reaction oxidizes the metal. Possible fluxes include SiO _Two , FeO, CaO, MgO, Na _Two O or K _Two O is included. In addition, other materials such as tin compounds, tin ores, or other materials such as iron compounds or ores may be added to compensate for the loss of metal value. In a particularly preferred embodiment, tin ore (SnO _Two ) Is injected into the reactor to make up for tin loss.
[0074]
Hydrogen-containing gas containing hydrogen and excess steam is removed from reactor 602. The hydrogen-containing gas can pass through the waste heat boiler 606 to provide heat for additional steam, thereby saving heat value. Further, the hydrogen-containing gas flow gas includes tin oxide suboxide (SnO) and tin hydrate suboxide (SnO _Two H _Two ), And may contain some contaminants, such as particles of slag that has been volatilized or discharged (frozen) from the molten metal bath and slag, which can be removed at the baghouse 616. It is. For example, volatile tin compounds can be condensed from a gas stream and trapped in a waste heat boiler or baghouse with the particulate slag. After capture, these materials pelletize 618 and, in some cases, reactor 602 operating in a steam reduction mode, or in a metal oxide reduction mode, for recovery of metal number and control of slag chemistry. It can be provided to any of the operating reactors 604. After removal of the contaminants, the hydrogen gas stream is optionally treated in a condenser 620 and / or a cooler (not shown) to condense excess vapors from the hydrogen gas stream and provide high purity hydrogen gas. A stream 622 is generated. Water condensed from the hydrogen gas stream can be recycled for additional steam production.
[0075]
At the same time, the metal oxide is reduced in reactor 604. The metal oxide is reduced with a reducing agent, such as CO, which can be generated by injecting coal 624 (or other carbonaceous material) and oxygen 626 through tip immersion lance 628. For reactor 602, a tip immersion lance 628 provides good agitation and contact surface area between the reactants. Hydrogen-containing gas must also be injected using a tip immersion lance or similar device. The particulate coal can be added to the reactor 604 by other means, such as simply charging the coal into the reactor.
[0076]
Ash-forming minerals, which are typically part of coal (or other carbonaceous materials) used with oxygen to effect reduction of reactive metal oxides, contribute to the slag layer in reactor 604. If coal 624 is used and there is sufficient calcium oxide (CaO) in the slag, the slag layer can be a commercial pozzolan by-product. With respect to reactor 602, other materials, such as flux, can be injected into reactor 604 to control slag properties, such as, for example, slag flow or foamability.
[0077]
The exhaust gas from metal oxide reduction reactor 604 may include some contaminants from coal, such as carbon dioxide, nitrogen, and sulfur. Heat from the exhaust gas is stored in a waste heat boiler 610 that generates steam. The gas stream can then be processed in a baghouse 630 to remove particulate contaminants. The remaining gas can be processed in a limestone scrubber 632 to produce gypsum from environmentally friendly flue gas and sulfur from coal. Alternatively, sulfur can be treated with anhydrous ammonia to produce ammonium sulfide, a compound useful as a soil fertilizer.
[0078]
In this way, once the iron has been removed from the molten metal mixture in the steam reduction reactor 602 and the iron oxide has been reduced to iron in the metal oxide reduction reactor 604, their flow into and out of the reactor is switched by switching them. It is possible to reverse the function. Prior to switching the gas flow, the reactor can optionally be purged to remove residual gases and contaminants. Therefore, hydrogen gas can be produced substantially continuously.
[0079]
The hydrogen gas produced by the present invention is preferably of high purity. Preferably, the gas stream contains at least about 30% by volume of hydrogen of the residual compound, consisting mainly of water in the form of steam. After removing residual water with a condenser, the purity of hydrogen is preferably 99% or more, more preferably 99.9%. The hydrogen gas is carbon monoxide and carbon dioxide, as in the case of hydrogen produced by either methane steam reforming or coal gasification, either of two methods that make up the majority of hydrogen currently produced. It is an advantage of the present invention that there is no need to separate from other gaseous chemicals such as carbon. If a carbon material (eg, CO) is initially present in the gas stream due to carbon dissolved in the molten mixture, the gas is withdrawn and the fuel value is reduced until the hydrogen purity reaches a sufficient level. It is possible to burn for. That is, all dissolved carbon reacts preferentially with steam to produce CO before large amounts of hydrogen are produced by oxidation of the reactive metal. Further, the method and apparatus of the present invention allows for the production of large amounts of pure hydrogen gas at low cost. Hydrogen gas has a fuel value of about 51,623 BTU / lb (13,009 kcal) and is useful as a component of combustion gases. Hydrogen can also be used in hydrogenation processes and semiconductor manufacturing. Further, it can be directly used as a fuel for a fuel cell such as a proton exchange membrane fuel cell (PEMFC).
[0080]
One aspect of the present invention is directed to the treatment of coal to produce energy values from coal, while minimizing emissions of harmful by-products of the coal, typically associated with energy conversion, to the atmosphere. The method allows extracting available content of energy in the form of intermediate BTU gas from coal while minimizing the release of harmful by-products to the atmosphere.
[0081]
Coal is relatively abundant in the United States and in many other areas, including third countries where energy production infrastructure is developing. One of the problems with the use of coal is that coal generally contains sulfur, whose mineral content must be cleaned or removed, and nevertheless usually burned to meet environmental standards. Post-gas cleaning is additionally required.
[0082]
One of the advantages of the present invention is that the coal feedstock may include lower coals, including high sulfur coals, and other lower coals. These lower grade coals are readily available and available at low cost. As used herein, the term "low coal" refers to coal having a sulfur content greater than 2% by weight and an ash content greater than about 10% by weight.
[0083]
In general, the method of the present invention provides a coal feed to a hydrogenation unit, and the coal feed is made from H _Two And contacting with a processing gas containing. Hydrocarbons in volatile coal react with hydrogen to produce methane (CH _Four ). The exhaust gas from the hydrogenation unit can be cleaned if necessary to produce a clean high BTU gas product. Some of this gaseous product can be burned in a combined cycle generator, taking advantage of the high thermo-electric conversion efficiency of the generator. Other parts of the gaseous product can be combusted in a conventional boiler with the non-volatile carbon generated in the hydrogenation unit. Since the hydroprocessing gas is a strong desulfurizer, the carbon is substantially free of sulfur. In one embodiment, other portions of the carbon produced in the hydrogenation unit can be recycled back to the metal oxide reduction step, where the metal oxide is reduced to a reactive metal. In this way, the coal is advantageously separated into volatiles (treated with hydrogen) and fixed carbon (reacted with oxygen).
[0084]
Referring to FIG. 7, coal 702 is first conveyed, possibly with other organics, to a preheater 704 that increases the temperature of the coal. The heated coal is then transported to a hydrogenation unit 706, where the coal contacts the hydrogen gas 705 generated by the method described above.
[0085]
Hydrogenation unit 706 can be a fluidized bed reactor or other reactor suitable for treating particulate coal. Unit is about 5 psi (351 g / cm ^Two It is preferred to operate at or near atmospheric pressure, such as at the following pressures:
[0086]
It is a cost advantage of the present invention that the hydrogenation unit 706 does not operate at significantly higher pressures. Significantly higher pressures produce additional methane, a gas containing a very high BTU. However, in order to convert coal to clean energy, it is more cost effective to produce combustible gaseous carbon monoxide and hydrogen from coke, which is the residue of the hydrogenation process. Coke and steam (CO and H _Two The gas derived from the reaction between (1) and (2) combines with methane from the hydrogenation to produce a valuable intermediate BTU gas. The reaction in the hydrogenation unit 706 is preferably performed at at least about 700 ° C, and preferably does not exceed about 1100 ° C, such as from about 800 ° C to about 900 ° C. The reactions that take place in the hydrogenation unit are exothermic and the need for additional external heat is minimal.
[0087]
Coal is a complex mixture of chemical compounds, mainly organic compounds. Coal is largely hydrocarbon, but impurities such as sulfur and nitrogen are trapped in the coal. These impurities, which are released when coal is burned, produce sulfuric acid and nitric acid when released to the atmosphere, and must be cleaned from off-gas in typical coal-based power plants. In addition, when coal burns, carbon combines with atmospheric oxygen to form CO2 _Two That is, it produces the well-known greenhouse gas that captures the heat of the earth.
[0088]
According to the present invention, when treating coal 702 with hydrotreating gas 705 in hydrogenation unit 706, the coal does not burn. Rather, it is heated to remove volatile components in the coal. These volatile components advantageously produce a high BTU product gas consisting mostly of methane. The remaining volatiles are purified by the action of hydrogen, which includes removal of sulfur and nitrogen. The resulting purified carbon (e.g., coke 707) is converted to carbon monoxide and hydrogen (a) which burns with methane in a conventional boiler without producing harmful excess by-products. The gas is added to methane from hydrogenation reactor 706 to produce an intermediate combustion BTU gas, (c) to produce activated carbon 716 activated by oxygen and steam, or (d) a combination thereof. I do.
[0089]
The methane-containing gas stream produced from the hydrogenation reaction can preserve the heat value from the gas stream through the waste heat boiler 708. Thereafter, it is possible to remove contaminants such as sulfur from the methane-containing gas stream using limestone, quicklime or an ammonia scrubber, thereby producing a high-purity methane-containing gas 712. The sulfur in the coal is hydrogen sulfide (H _Two S), which can be scrubbed from the methane gas stream. In some cases, it is advantageous to scrub the methane gas stream prior to combustion, as combustion produces a large gas stream.
[0090]
The methane gas can be burned on site to generate electricity, or can be stripped of CO (if any) and provided to the end user as pipeline gas. Further CH _Four Can be circulated back to other unit operations to provide processing heat. For example, CH _Four Can be bypassed to the steam superheater 714.
[0091]
The hydrotreating advantageously removes impurities in the coal 702 and produces a clean coke product 707. The coke product 707 can be processed in an activation / oxidation unit 718 if necessary, including (a) activated clean carbon 716, (b) clean coke, (c) hydrogen and Produce a gas mixture consisting of carbon oxide, or (d) some combination of the foregoing.
[0092]
According to one embodiment of the present invention, a portion of coke 707 can be circulated back to the metal oxide reduction reactor (FIG. 5) to reduce metal oxide. The carbon is converted to CO and ash incorporated into the slag, which can be removed periodically. The remaining coke from the hydrogenation unit 706 can be burned with methane for additional energy production in a conventional boiler.
[0093]
Further, a portion of the hydrogen gas 705 produced by the reduction of the steam can be bypassed from the hydrogenation unit 706 and used alone or in combination with methane gas as a direct fuel source. For example, hydrogen can be burned directly in boilers, internal combustion engines, or fuel cells.
[0094]
As mentioned above, the primary feed to the hydrogenation unit of the present invention can be a low grade coal as well as a high grade coal. In fact, lower coal feedstocks are advantageous because they are generally available at lower cost. In one embodiment, it is preferably a lower coal having at least 1% by weight of sulfur, more preferably at least 2% by weight of sulfur. Coal can be pulverized to remove water and the like. For example, it is desirable to pulverize the coal so that the maximum particle size does not exceed about 1 mm. If the raw material is pulverized coal, the hydrogenation process will yield a finely divided and finely divided carbon product.
[0095]
By the hydrotreating of the present invention, volatiles (for example, hydrocarbons) in coal are converted to methane. Preferably, at least about 90% by weight of the volatiles is converted to methane, more preferably at least about 95% by weight, and even more preferably at least about 99% by weight.
[0096]
As mentioned above, coal often contains pollutants that contain high levels of sulfur. The process of the present invention advantageously and immediately removes contaminants from the volatiles portion of the coal as well as residual coke. For example, sulfur reacts with hydrogen gas to produce hydrogen sulfide, which can be easily removed from waste streams.
[0097]
In addition, the method of the present invention allows for the production of energy from coal feedstocks while at the same time producing much less carbon dioxide per kilowatt-hour of energy produced than typically produced in conventional coal-fired power plants. . This low ratio of carbon dioxide to kilowatt-hours of power generated is a natural occurrence as the process of the present invention converts solid fuel coal to intermediate BTU gaseous fuel. The thermoelectric conversion efficiencies (expressed in%) of solid fuels range from the mid-20s to early 30s, while the thermoelectric conversion for gaseous fuels is 55-60%. Reduction in carbon dioxide emissions is an important environmental factor and adds further value to the process.
[0098]
As mentioned above, the carbon produced in the hydrogenation unit is activated carbon. Activated carbon is in an amorphous form characterized by high adsorption of many gases, vapors and colloidal solids. The internal surface area of activated carbon is several hundred m ^Two / G and a density of about 0.85 g / cm ^Three Does not exceed. Activated carbon has high value, including air and water purification, waste disposal, mercury (Hg) and flue gas from flue gas. _x Can be used for the removal of Thus, the hydrogenation process, when applied to coal, provides a high BTU gas stream as well as valuable by-products.
[0099]
In addition to coal, other hydrocarbon-containing raw materials are similarly treated to produce methane (CH _Four ) Can be produced. The feed is fed to a hydrogenation unit where a portion of the feed is CH _Four To convert to _Two At high temperatures with large amounts of gas compositions containing
[0100]
One advantage of the present invention is that the feed can be very low cost, or virtually any hydrocarbon containing feed, including those available at a negative total cost.
[0101]
In one embodiment, the raw material is municipal waste. Municipal waste may include household and industrial waste, hazardous waste, animal waste, sewage sludge, automotive shredded waste (ASR), rubber tire debris, and the like. Municipal waste is usually available at a negative total cost, as the municipality pays a "care" fee for the removal and destruction of waste.
[0102]
According to the United States Environmental Protection Agency, the United States generated 220 million tons of municipal waste in 1998. Per capita waste from 2.7 pounds (1.226 kilograms) per person in 1960 to 3.7 pounds (1.680 kilograms) per person in 1980, 4 per person per day in 1998 It has steadily increased to 0.5 pounds. The components of US municipal waste according to the 1998 EPA (prior to regeneration) are shown in Table 3.
[0103]
[Table 3]

[0104]
If the raw material is municipal waste, the raw material can be processed and separated if necessary. For example, magnetic metals such as iron and steel can be easily removed and sold as scrap. In some cases, cellulose-based materials (eg, paper and wood) can also be removed from the feed to reduce the level of oxygen compounds in the feed. For example, air separation can be used to separate this light, relatively dry waste portion, including paper and cardboard, garden trim and wood, for example. Remaining waste, including food waste, plastics, rubber, leather, non-ferrous metals, and glass, can be separated by water classification. Non-ferrous metals and glass can be recycled elsewhere.
[0105]
As mentioned above, the term "municipal solid waste" may include not only resident and municipal industrial waste, but also automotive shredded waste (ASR) and "cotton fluff". Recycled vehicle ASR, which is primarily a non-ferrous metal component, is a heterogeneous mixture of plastic, rubber, fiber, unrecovered metal and mud. The plastic content of ASR is typically about 20% by weight, and increases as the amount of plastic used in automobile manufacturing increases. The ASR is now burying the ground, and in some areas legislation has been proposed for ASR as a hazardous waste that has dramatically increased the cost of disposal. Therefore, converting ASR to a useful product gas would be a significant environmental and environmental protection remedy.
[0106]
Like coal, municipal waste can be separated into volatiles and fixed carbon using heat. The chemical composition of volatiles from municipal waste is generically CH _x Can be represented by That is, the reaction that occurs when waste contacts large amounts of hydrogen gas in the hydrogenation unit can be described as follows.
0.5 (4-x) H _Two + CHx → CH _Four (9)
[0107]
Advantageously, large quantities of combustible gas are produced by the waste and the method of the invention. One ton of municipal waste can generate about 48,550 cubic feet (1,374 cubic meters) of gas, including about 19,900,000 BTU (5,014,800 kcal). The gas consists of about 82% carbon monoxide, 16% methane and 2% hydrogen and contains about 410 BTU per cubic foot (about 3,690 kcal per cubic meter).
[0108]
According to other embodiments, the feed can be a hydrocarbon-containing material, including crude oil, tar sands or the like. Crude oil is a mixture of liquid hydrocarbons and various petroleum products collected from the earth's crust for use as fuel. Because crude oil is a mixture of widely varying components and proportions, its physical properties vary widely and many crude oils are of low value due to the inclusion of contaminants in the oil. The present invention advantageously allows the lower crude to be processed to produce useful gas products.
[0109]
Tar sands, also called bituminous sands, are sediments of coarse sand or partially solidified sandstone saturated with high viscosity bitumen. Oil recovered from tar sands is commonly referred to as synthetic crude, potentially in the form of mostly fossil fuels. However, recovering oil from tar sands is difficult and costly. The invention makes it possible to produce useful gas products from tar sands of low value.
[0110]
It will also be appreciated that two or more of the above components may be used in combination as raw materials. For example, it is possible to supplement finely divided coal to the separated municipal waste stream.
[0111]
Yet another aspect of the invention is directed to the production of ammonia using hydrogen gas and nitrogen gas as reactants. One important aspect of the method of the present invention is to produce large amounts of hydrogen gas in situ at relatively low cost. It is believed that one of the major obstacles to the methods disclosed in the prior art for producing ammonia is the high cost associated with large amounts of hydrogen gas and hydrogen gas. According to the present invention, a large amount of hydrogen gas is produced economically in situ.
[0112]
According to the present invention, nitrogen and hydrogen are converted to ammonia (NH _Three H) to maximize production _Two : N _Two Are combined in a molar ratio of about 3: 1. In a typical method for producing ammonia, a gas containing hydrogen and nitrogen is compressed to a pressure of about 200 atmospheres and passed over an iron catalyst at a temperature of about 380C to about 450C.
[0113]
A method for producing ammonia incorporating the method for producing hydrogen and nitrogen gas described above is shown in FIG. To produce hydrogen, water 801 is provided to a boiler 802 and steam is provided to one of the reactors 810 or 812. The hydrogen gas then passes through a condenser 820 to remove water and is then provided to an ammonia synthesis loop 848.
[0114]
At the same time, air 800 is supplied to the oxidation reactor 811 to remove oxygen from the air and provide a nitrogen gas stream 825. In the embodiment illustrated in FIG. 6, reactor 811 is a metal oxidation reactor, while reactor 813 is a metal oxide reduction reactor. A single reactor may be advantageously used to provide the reducing gas for both hydrogen production and nitrogen production unit operation.
[0115]
In this manner, hydrogen gas 824 and nitrogen gas 825 are provided to the ammonia synthesis loop 848. Preferably, the ammonia synthesis loop operates at a high pressure, up to about 200 atmospheres. In addition, the ammonia synthesis loop 848 can be operated at elevated temperatures and include a catalyst. Ammonia production from hydrogen and nitrogen has been described by McCarroll et al. In U.S. Pat. No. 4,600,571 and Pinto et al. In U.S. Pat. No. 4,298,588. U.S. Pat. No. 4,088,740 to Gaines et al. All of the aforementioned U.S. patents are incorporated herein in their entirety.
[0116]
The resulting ammonia can be used for many applications. For example, ammonia can be converted to urea for use in fertilizers. Ammonia also emits NO from coal-fired power plants. _x Used to reduce emissions and can be used to produce various ammonia-containing compounds.
[0117]
While various embodiments of the present invention have been described in detail, it will be apparent that those skilled in the art can make modifications and adaptations. However, it should be particularly understood that modifications and adaptations are within the spirit and scope of the invention.
[Brief description of the drawings]
[0118]
FIG. 1 is a phase diagram of a binary tin-iron metal mixture useful in the present invention.
FIG. 2 illustrates hydrogen production rate as a function of iron content according to one embodiment of the present invention.
FIG. 3 illustrates the rate of hydrogen production as a function of iron content and reaction temperature according to one embodiment of the present invention.
FIG. 4 shows a reactor operating in a steam reduction mode according to one embodiment of the present invention.
FIG. 5 illustrates a reactor operating in a metal oxide reduction mode according to one embodiment of the present invention.
FIG. 6 is a flow chart of a continuous hydrogen production process of the present invention.
FIG. 7 is a flow chart of a coal or other organic-containing raw material processing step of the present invention.
FIG. 8 is a flowchart of an ammonia production process of the present invention.

Claims (89)

In a method for producing a hydrogen-containing gas stream,
(A) generating steam;
(B) contacting the vapor in a reactor with a molten metal mixture comprising at least about 20% by weight of iron dissolved in a first diluent metal, wherein at least a portion of the iron is bound to iron oxide. Oxidizing, at least a portion of the steam is reduced to produce hydrogen, contacting the steam;
(C) extracting the hydrogen-containing gas stream from the reactor. The method of claim 1, wherein the molten metal mixture further comprises a second reactive metal. The method of claim 1, wherein the first diluent metal is selected from the group consisting of tin, copper and nickel. The method of claim 1, wherein the first diluent metal is tin. The method of claim 1, wherein the molten metal mixture further comprises a second diluent metal. The method of claim 1 wherein solid particles of iron are dispersed in the molten metal mixture. The method of claim 6, wherein the molten metal mixture is at a temperature between about 895C and about 1134C during the steam contacting step. The method of claim 1, wherein the molten metal mixture is at a temperature less than about 1538C during the steam contacting step. The method of claim 1, wherein the molten metal mixture is at a temperature no greater than about 1400C during the steam contacting step. The method of claim 1, wherein the molten metal mixture is at a temperature of about 1134C to about 1300C during the steam contacting step. The method of claim 1, wherein the molten metal mixture is at a temperature from about 1200C to about 1300C during the steam contacting step. The method of claim 1, wherein the hydrogen-containing gas stream comprises at least 30% by volume of hydrogen gas. The method of claim 1, further comprising withdrawing water from the hydrogen-containing gas stream. The method of claim 1, wherein the steam contacting step comprises injecting steam into the molten metal mixture using a tip dipping lance. The method of claim 1, further comprising contacting the iron oxide with a reducing agent to reduce the iron oxide to iron. The method of claim 1, further comprising adding a flux to the molten metal mixture to promote formation of a slag layer on the molten metal mixture. Adding a flux selected from the group consisting of SiO ₂ , FeO, CaO, MgO, Na ₂ O, K ₂ O and mixtures thereof to the molten metal mixture to form a slag layer on the molten metal mixture. The method of claim 1, further comprising the step of promoting. In a method for producing a hydrogen-containing gas stream,
(A) generating steam;
(B) contacting the vapor in a reactor with a molten metal mixture comprising a first reactive metal dissolved in a first diluent metal, wherein the molten metal mixture is brought to a temperature of at least about 1100 ° C. Contacting the steam, wherein at least a portion of the first reactive metal is oxidized to a first metal oxide and at least a portion of the steam is reduced to produce hydrogen;
(C) extracting the hydrogen-containing gas stream from the reactor. 19. The method of claim 18, wherein the molten metal mixture is at a temperature of at least about 1134C. 19. The method of claim 18, wherein the molten metal mixture is at a temperature below the pure melting point of the first reactive metal during the vapor contacting step. 19. The method of claim 18, wherein the molten metal mixture is at a temperature no higher than about 1400C. 19. The method of claim 18, wherein the molten metal mixture is at a temperature between about 1200C and about 1300C during the steam contacting step. 19. The method of claim 18, wherein said molten metal mixture comprises at least about 3% by weight of said first reactive metal. 19. The method of claim 18, wherein said molten metal mixture comprises at least about 10% by weight of said first reactive metal. 19. The method of claim 18, wherein said molten metal mixture comprises at least about 20% by weight of said first reactive metal. 20. The method of claim 18, wherein said first reactive metal is selected from the group consisting of iron, tin, tungsten, germanium, molybdenum, indium, zinc, cobalt, and antimony. 19. The method of claim 18, wherein said first reactive metal is iron. 19. The method of claim 18, wherein said molten metal mixture further comprises a second reactive metal. 19. The method of claim 18, wherein said first diluent metal is selected from the group consisting of tin, copper and nickel. 19. The method of claim 18, wherein said diluent metal is tin. 19. The method of claim 18, wherein said molten metal mixture further comprises a second diluent metal. 19. The method of claim 18, wherein said hydrogen-containing gas stream comprises at least about 30% by volume of hydrogen gas. 19. The method of claim 18, further comprising withdrawing water from the hydrogen-containing gas stream. 19. The method of claim 18, wherein said steam contacting step comprises injecting steam into said molten metal mixture using a tip dipping lance. 20. The method of claim 18, further comprising reducing the first metal oxide to the reactive metal. 20. The method of claim 18, further comprising adding a flux to the molten metal mixture to promote slag layer formation. The molten metal mixture, SiO _2, FeO, in addition CaO, MgO, Na ₂ O, the flux is selected from K ₂ O and mixtures thereof, to promote the production of slag layer on the molten metal mixture 19. The method of claim 18, further comprising the step of: In a method for producing a hydrogen-containing gas stream,
(A) generating steam;
(B) contacting the vapor in a reactor with a molten metal mixture comprising a first reactive metal dissolved in a first diluting metal, wherein the reactive metal-containing particles are contained in the molten metal mixture; At least a portion of the first reactive metal dispersed and dissolved in the diluting metal is oxidized to a first metal oxide, and at least a portion of the vapor is reduced to produce hydrogen, wherein the vapor is contacted Process and
(C) withdrawing the hydrogen-containing gas stream from the reactor;
A method for producing a hydrogen-containing gas stream, wherein when the first reactive metal is oxidized, the reactive metal-containing particles are at least partially dissolved in the molten metal mixture. 39. The method of claim 38, wherein the first reactive metal is selected from the group consisting of iron, tin, tungsten, germanium, molybdenum, indium, zinc, cobalt, and antimony. 39. The method according to claim 38, wherein said first reactive metal is iron. 39. The method of claim 38, wherein said molten metal mixture further comprises a second reactive metal. 39. The method of claim 38, wherein said first diluent metal is selected from the group consisting of tin, copper and nickel. 39. The method of claim 38, wherein said diluent metal is tin. 39. The method of claim 38, wherein the molten metal mixture further comprises a second diluent metal. 39. The method of claim 38, wherein said first reactive metal is iron and said first diluent metal is tin. 39. The method of claim 38, wherein said molten metal mixture is saturated with said first reactive metal. 39. The method of claim 38, wherein said reactive metal-containing particles are metal particles. 39. The method of claim 38, wherein the molten metal mixture is at a temperature between about 895C and about 1134C during the steam contacting step. 39. The method of claim 38, wherein the hydrogen-containing gas stream comprises at least 30% by volume of hydrogen gas. 39. The method of claim 38, wherein the steam contacting step comprises injecting steam into the molten metal mixture using a tip dipping lance. 39. The method of claim 38, further comprising contacting the first metal oxide with a reducing agent to reduce the first metal oxide to the first reactive metal. 39. The method of claim 38, further comprising the step of adding a flux to the molten metal mixture to promote the formation of a slag layer over the molten metal mixture. A flux selected from the group consisting of SiO ₂ , FeO, CaO, MgO, Na ₂ O, K ₂ O and mixtures thereof is added to the molten metal mixture to promote the formation of a slag layer on the molten metal mixture. 39. The method of claim 38, further comprising the step of: In a method for producing a hydrogen-containing gas stream,
(A) generating steam;
(B) contacting the steam with a molten metal mixture consisting of molten iron dissolved in molten tin in a reactor, wherein the steam reacts with the molten iron to produce hydrogen and iron oxide;
(C) extracting the hydrogen-containing gas stream from the reactor. 55. The method of claim 54, wherein said molten metal mixture is at a temperature of at least about 1134C during said steam contacting step. 55. The method of claim 54, wherein said molten metal mixture is at a temperature of about 1400C or less during said steam contacting step. 55. The method of claim 54, wherein said molten metal mixture is at a temperature of about 1200C to about 1300C during said steam contacting step. 55. The method of claim 54, wherein the molten metal mixture comprises at least about 3% by weight of the molten iron dissolved in the molten tin. 55. The method of claim 54, wherein said molten metal mixture comprises at least about 10% by weight of said molten iron dissolved in said molten tin. 55. The method of claim 54, wherein said contacting step comprises injecting steam into said molten metal mixture using a tip dipping lance. 55. The method of claim 54, wherein iron from the iron-containing particles dissolves in the molten metal mixture when iron-containing particles are dispersed in the molten metal mixture and the steam reacts with the molten iron. 62. The method of claim 61, wherein the molten metal mixture is at a temperature between about 895C and about 1134C during the steam contacting step. The method of claim 54, wherein the hydrogen-containing gas stream comprises at least 30% by volume of hydrogen gas. 55. The method of claim 54, further comprising withdrawing water from the hydrogen-containing gas stream. In the method for producing hydrogen gas,
(A) contacting a vapor in a reactor with a molten metal mixture comprising a first molten reactive metal dissolved in a first molten diluting metal, wherein at least a portion of the first reactive metal is a first molten metal; Oxidizing to a metal oxide of to produce a hydrogen-containing gas stream;
(B) extracting the hydrogen-containing gas stream;
(C) reducing the first metal oxide to the first reactive metal in the reactor by injecting particulate coal and an oxygen-containing gas into the reactor. Gas production method. 66. The method of claim 65, wherein said reducing step comprises injecting coal and an oxygen containing gas into said reactor. 66. The method of claim 65, wherein the reducing step comprises injecting coal and an oxygen containing gas into the reactor through a dip lance. 66. The method of claim 65, wherein said first reactive metal is iron. 66. The method of claim 65, wherein said first diluent metal is tin. 67. The method of claim 65, wherein said first reactive metal is iron and said diluent metal is tin. 66. The method of claim 65, wherein the molten metal mixture is at a temperature of at least about 1134 [deg.] C during the steam contacting step. 66. The method of claim 65, wherein during the steam contacting step, the molten metal mixture is at a temperature from about 1200 <0> C to about 1300 <0> C. 66. The method of claim 65, wherein the steam contacting step comprises injecting steam into the molten metal mixture using a tip dipping lance. 66. The method of claim 65, further comprising adding a flux to the molten metal mixture to promote slag layer formation. The molten metal mixture, according to _{SiO 2, FeO, CaO, MgO} , Na 2 O, adding a flux selected from the group consisting of K ₂ O, claim 38, further comprising the step of promoting the generation of the slag layer the method of. In a method for producing a hydrogen-containing gas stream,
(A) generating steam;
(B) forming a slag layer comprising a hydrogen-containing gas stream and iron oxide on top of the molten metal mixture in a molten metal mixture contained in a reactor comprising molten iron dissolved in molten tin; Injecting under conditions sufficient to
(C) withdrawing the hydrogen-containing gas stream from the reactor;
(D) stopping the injection of the steam;
(E) injecting a particulate carbon source and an oxygen-containing gas into the reactor to reduce the iron oxide to metallic iron. 77. The method of claim 76, wherein the molten metal mixture is at a temperature of at least about 1134C. 77. The method of claim 76, wherein said steam injecting step comprises injecting steam using a tip immersion lance. 77. The method of claim 76, wherein the step of injecting the carbon source comprises injecting coal into the reactor. 77. The method of claim 76, further comprising adding a flux into the molten metal mixture to promote formation of the slag layer. The method of claim 76, further comprising: adding a flux selected from the group consisting of SiO ₂ , FeO, CaO, MgO, Na ₂ O, and K ₂ O to the molten metal mixture to promote formation of the slag layer. The described method. In a method for producing a hydrogen-containing gas stream,
(A) generating steam;
(B) injecting the steam into a molten metal mixture contained in a reactor, the molten metal mixture including a first molten metal dissolved in a second molten metal; Reacting with a metal to produce hydrogen and a first metal oxide having a density at least about 10% lower than the molten metal mixture, whereby the first metal oxide flows through the molten metal mixture in the molten metal mixture Ascending to a slag layer arranged above,
(C) extracting a hydrogen-containing gas from the reactor. 83. The method according to claim 82, wherein said first molten metal is iron. 83. The method according to claim 82, wherein said second molten metal is tin. (A) stopping the injection of the steam;
83. The method of claim 82, further comprising: (b) reducing the first metal oxide in the slag layer to the first molten metal and redissolving the first molten metal in the molten metal mixture. The described method. In the method of treating coal,
(A) generating a hydrogen-containing gas stream,
(I) generating steam;
(Ii) oxidizing a portion of the molten iron to iron oxide in the molten metal mixture contained in the first reactor, wherein the hydrogen-containing gas stream contains molten iron dissolved in molten tin; Injecting under conditions sufficient to produce
(Iii) generating the hydrogen-containing gas stream performed by a method comprising withdrawing the hydrogen-containing gas stream from the first reactor;
(B) contacting the hydrogen-containing gas stream with particulate coal in a second reactor at a temperature of at least about 700 ° C;
(C) withdrawing a methane-containing gas stream from said second reactor. 87. The method of claim 86, further comprising withdrawing coke product from said second reactor. 87. The method of claim 86, further comprising withdrawing coke product from the second reactor and injecting the coke product into the first reactor to reduce the iron oxide to iron. In the method for producing ammonia,
(A) generating a hydrogen-containing gas stream,
(I) generating steam;
(Ii) oxidizing a portion of the molten iron to iron oxide in the molten metal mixture contained in the first reactor, wherein the hydrogen-containing gas stream contains molten iron dissolved in molten tin; Injecting under conditions sufficient to produce
(Iii) generating the hydrogen-containing gas stream performed by a method comprising withdrawing the hydrogen-containing gas stream from the first reactor;
(B) A method for producing ammonia, comprising the step of contacting the hydrogen-containing gas stream with a nitrogen-containing gas stream to produce ammonia.

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