0 引 言

我国化石资源以煤炭为主,以煤基发电为代表的火力发电机组发电量占比长期超过50%。其中,整体煤气化燃料电池(Integrated Gasification Fuel Cell,IGFC)是双碳目标下煤炭发电的根本变革性技术,融合了洁净煤和调峰灵活性技术[1]。与整体煤气化联合发电技术(IGCC)[2]、超超临界发电技术[3]等相比,IGFC在发电效率提升、CO2捕集和减排方面具有更大优势[4-8]。国内IGFC领域研究起步相对较晚,相关代表机构有北京低碳清洁能源研究所、中国矿业大学(北京)、中国华能集团有限公司和中国神华能源股份有限公司等,主要从事IGFC部件开发及系统集成研究[9]。WEI等[10]对MWth级 IGFC示范系统进行模拟和分析,并采用煤气化合成气对20 kW SOFC机组进行测试,直流效率达50.41%;LI等[11]分别建立了基于E-Gas气化炉和壳牌气化炉2种炉型的MW级IGFC系统模型,并对2种IGFC系统进行能量分析。结果表明,E-Gas IGFC系统的直流发电效率和净效率分别为52.82%和50.89%,均高于壳牌IGFC系统的49.24%和49.74%;WANG等[12]应用仿真方法对燃烧室关键性能指标进行研究,通过试验进行验证。结果表明,获得火焰稳定性的理想冷凝温度为315 K,在纯氧火焰燃烧条件下,CO几乎完全转化,并建议氧气过量系数不低于5%以最大限度捕获CO2,促进IGFC与CO2捕集相结合的系统设计。

目前,与传统燃煤电站相比,IGFC系统在投资规模、经济性、技术成熟度等方面还有一定劣势[13-14]。由于煤制合成气成分复杂,且固体氧化物燃料电池(SOFC)对合成气中硫、氯等元素较敏感,深度脱除工艺往往导致整体能效降低,煤气化与燃料电池结合存在诸多困难。因此IGFC暂时还没有成熟的商业化应用,对IGFC系统研究多基于模拟[15-19]。

通常情况下,煤化工装置对合成气中硫、氯等元素同样有较高要求。甲醇合成装置中间气体中毒素含量低于煤制合成气,使煤气化化工与SOFC结合更现实可行。为加快IGFC的工程化及商业化进程,必须基于投产的煤气化化工系统与燃料电池(简称FC)、燃气透平技术(简称GT)的复合系统,实现“化工品-热-电”联供,提高投产煤气化化工系统的经济性或能效。其中煤气化化工燃料电池发电与甲醇联产技术(Integrated Gasification Chemical Fuel Cell Power and Methanol Co-generation,IGFC-CMP)尤为重要。

笔者首先介绍所构建IGFC-PMC系统的基本流程,并对典型条件下系统化工品产出、电力和热力出力进行分析。在此基础上,针对气化炉关键参数对各关键部件出力、效率及其他运行参数的影响规律进行分析,为IGFC-PMC系统的设计及性能优化提供参考。

1 系统设计

选用山东能源集团旗下内蒙古荣信化工有限公司多喷嘴对置式水煤浆气化炉制取甲醇系统为研究对象,基于Aspen软件建立IGFC-PMC仿真模型,分析水煤浆系统参数变化对联合系统运行特性的影响。构建的系统工艺流程如图1所示,虚线框为原多喷嘴对置式水煤浆气化炉制取甲醇系统部分装置。

系统中,原煤经磨煤等预处理过程后与水混合,再由高压煤浆泵输送进入气化炉,在贫氧条件下发生反应,生成以CO、H2、CH4、CO2、H2O等为主要成分,同时含有H2S、灰渣等杂质的粗煤气,温度约1 300 ℃。粗煤气经若干换热器后,进入煤气冷却器(激冷)进行高品位热量回收,产生高压过热蒸汽,随后进入煤气净化单元。在煤气净化单元,降温后的粗煤气经过除尘、水洗、部分水汽变换、低温甲醇洗等过程去除其中粉尘和硫化物等杂质,得到净化气。净化气压力在5.5 MPa左右,经压缩机加压后,与循环气一道进入合成塔反应生成甲醇,塔出口为气汽混合物,以CH3OH、CH3CH2OH、N2、CO、H2、H2O、CH4、CO2等为主,经过气液分离后,得到以CH3OH、CH3CH2OH、H2O为主的粗甲醇。剩下的排气大部分作为循环气,经过再次加压后返回甲醇合成塔中,小部分作为驰放气,经过提纯装置进一步分离出富氢气,再返回循环气中,而非渗透气可进入燃料电池单元阳极,在约0.8 MPa压力下与进入阴极空气中的氧气发生电化学反应,将化学能直接高效转化为电能并产生热量。部分未反应的燃料气与反应后生成的CO2、H2O一起进入燃烧器燃烧后,进入透平回收部分能量。此外,为调节“化工品-热-电”间负荷,部分合成气通过抽气回路与非渗透气共同前往发电设备。

与传统IGFC-PMC系统相比,该系统通过燃料电池、燃气透平利用甲醇合成装置的排气发电,同时,利用粗煤气加热抽气、燃料电池阳极和阴极气体,可实现能量梯级利用,能源利用效率更高。其次,如果燃料电池阳极烟气经热量回收后,直接前往CO2捕集装置,不参与混合燃烧及透平做功过程,CO2捕集效率更高。本次讨论中暂不考虑CO2捕集问题,电池阳极排气参与混合燃烧及透平做功,以求整体效率最大化。

系统所用原料煤的工业分析和元素分析见表1。

2 数学模型

燃料电池主要发生的反应为

2CO O22CO2,

(1)

2H2 O22H2O。

(2)

燃料电池发电效率nSOFC[20]为

(3)

式中,Uf为燃料电池阳极燃料利用率;PSOFC为燃料电池功率,MW;ΔHa为阳极进出口流体焓差,MW。

系统中透平1和透平2为燃气透平,其做功功率PGT[21]为

PGT=ΔHtηm,

(4)

式中,ΔHt为阳极进出口流体焓差,MW;ηm为机械效率,取0.99。

系统整体效率nsys为

(5)

式中,QMEOH甲醇低位热值,MJ/mol;FmoleMEOH为甲醇摩尔流量,mol/s;Ptub1、Ptub2分别为透平1和2的功率,MW;Pheat为系统余热的供热功率,MW;Qcoal为甲醇低位热值,MJ/kg;Fmasscoal为煤炭质量流量,kg/s。

3 模型分析

3.1 基本设计参数

基于Aspen plus软件建立水煤浆气化甲醇生产装置与固体氧化物燃料电池系统模型,运用Boston-Mathias函数修正的Redlich-Kwong-Soave状态方程。模型基于以下设定:① 气化炉运行压力保持恒定;② 低温甲醇洗装置的净化气出口温度保持恒定;③ 透平1入口温度通过空气调节,不超过设计温度;④ 燃料电池阳极燃料利用率及阴极氧气利用率保持恒定,电池设计参数见表2;⑤ 氢气回收装置的气体选择性保持恒定,具体参数见表3。

在典型操作条件下,进入重要部件的气体组成见表4,经模型计算,得出系统设计参数见表5。由表5可知,系统设计参数相对原生产数据误差较小,模型准确度较高。其中,粗煤气激冷前温度与生产数据差别较大,是由于粗煤气部分热能用于加热抽气、燃料电池阳极和阴极气体,温度降低。但该温度处于气化炉安全运行温度范围内(1 200～1 350 ℃),不存在气化炉低温积渣等安全风险。其次,相比原生产数据,电力输出总计增加9.77 MW,供热输出增加0.01 MW,系统整体效率从57.71%提高至59.22%,说明新系统在能源利用效率的优越性。

在非典型操作条件下,影响IGFC-PMC系统运行特性的因素包括煤质(灰分、灰熔融温度、水分)、运行条件(水煤比、氧煤比、气化温度、气化压力、有效气成分)等,也包括气化炉型、化工品装置、氢回收工艺等,影响因素较多。基于内蒙古荣信化工有限公司生产数据,结合IGFC-PMC系统技术特点,选取水煤浆浓度、净化气抽气占比2个因素为变量,讨论系统运行特性的变化规律。

3.2 水煤浆浓度的影响

水煤浆浓度nwc是关系气化炉效率及安全运行的重要参数,其定义为

(6)

式中,Fmasswater为给水的质量流量,kg/s。

水煤浆浓度对系统各项参数的影响如图2所示。水煤浆提浓是保持投煤量不变,调节水量实现。由图2(a)可知,水煤浆浓度由55%提升至60%时,气化炉反应温度由1 200 ℃上升至1 350 ℃,并带动燃料电池阳极、阴极入口温度及透平入口温度上升。阳极入口温度由858 ℃上升至1 010 ℃,阴极入口温度由810 ℃上升至960 ℃,透平入口温度由956 ℃ 上升至1 020 ℃。此时,燃料电池效率、燃料电池和透平1的功率随温度升高而升高,而供热功率变化不大。由图2(b)～图2(c)可知,燃料电池电压由0.58 V上升至0.92 V,效率由42.46%上升至68.42%,燃料电池输出功率由2.65 MW上升至4.22 MW;透平1功率由6.23 MW上升至6.56 MW。由于受限于水煤浆浓度变化幅度以及甲醇总热值占比较高,系统整体效率提升较小(59.05%提升至59.33%)。

3.3 净化气抽气占比的影响

通过抽取部分合成气调节发电流量,可以实现“化工品-热-电”供给调节。定义净化气的抽气占比nbg为

(7)

式中,Fmolebg为净化气抽气的摩尔流量,mol/s;Fmoleig为非渗透气的摩尔流量,mol/s。

净化气抽气占比对系统各项参数的影响如图3所示。发电燃料中净化气抽气流量由0上升至51.59% 时,燃料电池阳极、阴极入口温度以及透平入口温度几乎没有变化,此时燃料流量和摩尔组分变化是影响燃料电池、透平输出及甲醇产量的关键因素。发电燃料中净化气抽气占比由0上升至51.59% 时,虽然燃料电池阳极入口H2及CO等燃料摩尔分数上升,可减少电池极化损失,但燃料电池阳极流量增多及H2、CO摩尔分数增大(H2由37.93%增至54.10%,CO由14.65%增至22.53%),使电流密度从284.19 mA/cm2增至634.97 mA/cm2,是导致电池效率变化较大的原因(由58.00%降至37.04%)。由于做功流量增多,燃料电池及透平1、透平2的输出功率增大。甲醇合成装置的合成气总量减少,使甲醇产量减少。由于抽气量相对合成气总量不到2%,因此对甲醇产量影响较小,供热功率下降较小。由于系统发电输出功率增加,整体效率由59.20%上升至60.70%。

4 结 论

1)系统设计参数相对原生产数据误差较小,模型准确度较高。甲醇生产装置联合燃料电池发电,电力输出总计增加9.77 MW,供热输出增加0.01 MW,系统整体效率由57.71%提高至59.22%,说明新系统在能源利用效率方面具有优越性。

2)水煤浆浓度由55%提升至60%时,燃料电池效率、燃料电池和透平功率有所上升,对燃料电池功率和效率影响最大,整体效率提升较小。燃料电池效率由42.46%上升至68.42%,功率由2.65 MW上升至4.22 MW,透平1功率由6.23 MW上升至6.56 MW。系统整体效率由59.05%上升至59.33%。

3)抽气占比从0上升至51.59%时,由于抽气量相对合成气总量不到2%,因此对甲醇产量影响较小,供热功率下降较小。整体效率由59.20%上升至60.70%。因此,通过抽取部分净化气发电实现“化工品-热-电”的供给调节可行,建议通过设置并联备用机组实现发电机组扩容,以减少运行调控难度,维持燃料电池的高效率。

4)通过优化设计原甲醇生产系统,不仅提高了系统整体能效,也实现了从单一输出化工品、余热到“化工品-热-电”联供的转变,为缓解化工系统生产用电压力,优化产品多样性和经济性提供了新思路。

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Design and operation characteristics study of integrated coal gasification fuel cell power generation and methanol cogeneration system

SUN Shaodong1,LI Zhi1,2,YUAN Benfeng3,LI Yan′an1,LIU Yun1,LIU Xin1,LU Wenxue2,ZHANG Zhiwei2,LI Chengxin1

(1.State Key Laboratory for Mechanical Behavior of Materials,School of Materials Science and Engineering,Xi′an Jiaotong University,Xi′an 710049,China;2.National Engineering Research Center of Coal Gasification and Coal-based Advanced Materials,Shandong Energy Group Co.,Ltd.,Jinan 250000,China;3.Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Shanghai 201800,China)

Abstract：Based on the actual coal chemical system, the research on the coupling technology of coal gasification chemical industry, solid oxide fuel cell and gas turbine is a new idea to accelerate the engineering and commercial development of IGFC. The Inner Mongolia Rongxin Chemical multi-nozzle opposed coal water slurry gasification and methanol production system of Shandong Energy Group Co., Ltd. was designed to carry out the construction of coal gasification chemical engineering, solid oxide fuel cell, and turbine process flows by Aspen Plus, a chemical process analysis software. The effects of operating parameters on the integrated coal gasification fuel cell power generation and methanol co-generation (IGFC-PMC) system were studied by simulation calculation, and the chemical output, power and thermal output of the system under typical conditions were analyzed. On this basis, the influences of key parameters of gasifier on output, efficiency and other operating parameters of key components were analyzed. The results show that the methanol production unit combined with fuel cells can improve the overall efficiency of the system from 57.71% to 59.22%, indicating that the new system has advantages in energy utilization efficiency. When the concentration of coal water slurry increases from 55% to 60%, there is the greatest influence on the power and efficiency of fuel cells and little improvement on the overall efficiency. The efficiency of fuel cell increases from 42.46% to 68.42%, the power increases from 2.65 MW to 4.22 MW, and the power of turbine 1st increases from 6.23 MW to 6.56 MW. When the proportion of pumping gas increases from 0 to 51.59%, the impact on methanol production is small because the pumping volume is less than 2% relative to the total amount of syngas. In addition, the overall efficiency increases from 59.20% to 60.70%. It is feasible to adjust the supply of "chemicals, heat and electricity" by extracting part of the purified gas. It is suggested to expand the generator set by setting parallel standby units, so as to reduce the difficulty of operation regulation and maintain the high efficiency of fuel cells. The optimized design of the original methanol production system not only improves the overall energy efficiency of the system, but also realizes the transformation from a single output chemical and waste heat to the combined supply of chemical, heat and electricity, providing a new idea for chemical system to relieve the pressure of production electricity and product diversity and economic optimization.

Key words：gasification of coal water slurry to methanol;solid oxide fuel cell;gas turbine;integrated coal gasification fuel cell

中图分类号：TK91

文献标志码：A

文章编号：1006-6772(2023)03-0049-07

收稿日期：2023-03-11;

责任编辑:白娅娜

DOI：10.13226/j.issn.1006-6772.H23031101

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基金项目：国家重点研发计划资助项目(2021YFB4001400);山东能源集团重点科技资助项目(YKKJ2020B02XNY)

作者简介：孙少东(1990—),男,广东揭阳人,博士研究生。E-mail:stonesuen@stu.xjtu.edu.cn

通讯作者:李成新(1974—),男,河北乐亭人,教授,博士。E-mail:licx@mail.xjtu.edu.cn

引用格式：孙少东,李智,袁本峰,等. 整体煤气化燃料电池发电与甲醇联产系统运行特性[J].洁净煤技术,2023,29(3):49-55.

SUN Shaodong,LI Zhi,YUAN Benfeng,et al.Design and operation characteristics study of integrated coal gasification fuel cell power generation and methanol cogeneration system[J].Clean Coal Technology,2023,29(3):49-55.