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加氢过程必须通过标准化的加氢协议来规范。目前汽车行业采用的是美国汽车工程师协会SAE J2601[15]加氢协议,最新版本是2020年修订版。SAE J2601协议的范围包括水容积在49.7~248.6 L之间,压力等级为35 MPa和70 MPa的车载储氢瓶,以及大于248.6 L的70 MPa车载储氢瓶。
SAE J2601设定的加氢目标为3 min加满(SOC≥95%),同时加氢过程中车载储氢瓶内的氢气温度不得超过85 °C。为了同时满足加氢时间限制和温度限制,SAE J2601根据储氢瓶的压力等级、预冷温度等级、容量等级、环境温度和加氢前压力,规定了加氢终了压力和平均增压速率。
表1给出了一个70 MPa车载储氢瓶加氢前后的参数。根据SAE J2601 Table D28,该储氢瓶对应的加氢终了压力为86.8 MPa,平均增压速率为28 MPa/min。质量流量与压力对应,加氢过程中该车载储氢瓶压力和质量流量如图2所示。
表 1 车载储氢瓶加氢前后参数
Table 1. Parameters of onboard hydrogen storage cylinder before and after refueling
参数 水容积/L 温度/℃ 压力/MPa 氢气质量/kg 加氢前 141 10 10 1.14 加氢后 141 10 70 5.74 -
压缩机采用五级压缩中间冷却的方式,各级压缩的压比相等。第一级压缩的出口即第一级中间冷却的入口,五级中间冷却的冷量由冷水机组提供,使压缩过程尽可能接近等温压缩。各级压缩功率和中间冷却冷量分别为:
$$ {\dot W_{{\text{com}}}} = \dfrac{{{{\dot m}_{{\text{com}}}}({h_{{\text{com,in}}}} - {h_{{\text{com,out}}}})}}{{{\eta _{\text{s}}}{\eta _{{\text{el}}}}}} $$ (1) $$ {\dot Q_{\text{int} }} = {\dot m_{{\text{com}}}}({h_{{\text{int,in}}}} - {h_{{\text{int,out}}}}) $$ (2) 式中:
$\dot W_{\rm{com}}$ ——压缩机电功率(W);$\dot m_{\rm{com}}$ ——压缩机质量流量(kg/s);hcom,in
——压缩机入口氢气的比焓(J/kg); hcom,out ——压缩机出口氢气的比焓(J/kg);
$ {\eta }_{\mathrm{s}} $ ——绝热效率;$ {\eta }_{\mathrm{e}\mathrm{l}} $ ——电效率;$\dot Q_{\rm{int}}$ ——中间冷却冷量(W);hint,in
——中间冷却入口氢气的比焓(J/kg); hint,out
——中间冷却出口氢气的比焓(J/kg)。 冷水机组电功率为:
$$ {\dot W_{{\text{int}}}} = {{\left( {\displaystyle \sum\limits_{i = 1}^5 {{{\dot Q}_{{\text{int}}}}} } \right)} \mathord{\left/ {\vphantom {{\left( {\sum\limits_{i = 1}^5 {{{\dot Q}_{{\text{int}}}}} } \right)} {{\text{CO}}{{\text{P}}_{{int} }}}}} \right. } {\varepsilon_{\text{int} }}} $$ (3) 式中:
$\dot W_{\rm{int}}$ ——冷水机组电功率(W);εint ——冷水机组能效比。
长管拖车和3个高压储氢瓶的物理模型是一致的。通过质量守恒和能量守恒方程可以确定任一时刻储氢瓶内氢气的密度和比内能,从而可以确定其余的状态参数(温度、压力、比焓等)。储氢瓶的质量守恒方程为:
$$ {m_{{\text{cyl}}}}(t) = {m_{{\text{cyl}},0}} + \int {({{\dot m}_{{\text{cyl}},{\text{in}}}} - {{\dot m}_{{\text{cyl}},{\text{out}}}})} {\text{d}}t $$ (4) 式中:
mcyl ——储氢瓶氢气质量(kg);
t ——时间(s);
mcyl,0 ——储氢瓶初始状态氢气质量(kg);
mcyl,in ——储氢瓶入口氢气质量(kg);
mcyl,out ——储氢瓶出口氢气质量(kg)。
相应地,储氢瓶中氢气密度为:
$$ {\rho _{{\text{cyl}}}}(t) = {m_{{\text{cyl}}}}(t)/{V_{{\text{cyl}}}} $$ (5) 式中:
$ {\rho }_{\mathrm{c}\mathrm{y}\mathrm{l}} $ ——储氢瓶氢气密度(kg/m3);Vcyl ——储氢瓶体积(m3)。
储氢瓶的能量守恒方程为:
$$ \begin{split} &{m_{{\text{cyl}}}}(t){u_{{\text{cyl}}}}(t) = {m_{{\text{cyl}},0}}{u_{{\text{cyl}},0}}+ \int [{{\dot m}_{{\text{cyl}},{\text{in}}}}{h_{{\text{cyl}},{\text{in}}}} -\\& {{\dot m}_{{\text{cyl}},{\text{out}}}}{h_{{\text{cyl}},{\text{out}}}} - H{A_{{\text{cyl}}}}({T_{{\text{cyl}}}} - {T_{{\text{amb}}}})] {\text{d}}t \end{split} $$ (6) 式中:
$ {u}_{\mathrm{c}\mathrm{y}\mathrm{l}} $ ——储氢瓶氢气的比内能(J/kg);$ {u}_{\mathrm{c}\mathrm{y}\mathrm{l},0} $ ——储氢瓶初始状态氢气的比内能(J/kg);H ——对流传热系数[W/(m2·K)];
Acyl ——储氢瓶表面积(m2);
Tcyl ——储氢瓶氢气温度(K);
Tamb ——环境温度(K)。
高压储氢瓶的氢气流经减压阀的过程为等焓节流,减压阀的入口比焓即储氢瓶出口比焓:
$$ {h_{{\text{val,out}}}} = {h_{{\text{cyl,out}}}} $$ (7) 式中:
hval,out ——减压阀出口氢气的比焓(J/kg);
hcyl,out ——储氢瓶出口氢气的比焓(J/kg)。
减压阀后的氢气由于节流后升温,进入预冷换热器冷却至目标加注温度,预冷换热器所需冷量为:
$$ {\dot Q_{{\text{pre}}}} = {\dot m_{{\text{ref}}}}({h_{{\text{val,out}}}} - {h_{{\text{pre,out}}}}) $$ (8) 式中:
$\dot Q_{\rm{pre}}$ ——预冷换热器冷量(W);$\dot m_{\rm{ref}}$ ——加注质量流量(kg/s);hpre,out——预冷换热器出口氢气的比焓(J/kg)。
预冷换热器的冷量由冷冻机组提供,冷冻机组电功率为:
$$ {\dot W_{{\text{pre}}}} = {{{{\dot Q}_{{\text{pre}}}}} \mathord{\left/ {\vphantom {{{{\dot Q}_{{\text{pre}}}}} {{\text{CO}}{{\text{P}}_{{\text{pre}}}}}}} \right. } {\varepsilon_{{\text{pre}}}}} $$ (9) 式中:
$\dot W_{\rm{pre}}$ ——冷冻机组电功率(W);εpre ——冷冻机组能效比。
加氢过程的能耗主要由压缩机、冷水机组和冷冻机组3部分组成:
$$ Q = \int {({{\dot W}_{{\text{com}}}} + {{\dot W}_{{\text{int}}}} + {{\dot W}_{{\text{pre}}}})} {\text{d}}t $$ (10) 式中:
Q ——能耗(J)。
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氢气的物性通过查询REFPROP物性数据库得到,该物性数据库中的氢气数据来自真实气体状态方程[17],具有很高的准确度。加氢动态模型的求解逻辑为:(1)根据SAE J2601协议确定加氢压力、质量流量、温度,即确定了预冷换热器的出口状态;(2)根据级联高压储氢瓶的质量守恒和能量守恒,计算得到内部氢气的温度、压力、比焓,即确定了减压阀的入口状态和压缩机的出口状态;(3)根据等焓节流确定减压阀出口状态,从而确定了预冷量和冷冻机组能耗;(4)根据长管拖车的质量守恒和能量守恒,计算得到内部氢气的温度、压力、比焓,即确定了压缩机的入口状态;(5)根据压缩机入口压力和出口压力,计算各级压比、功率和需要的冷量,从而确定压缩机能耗和冷水机组能耗。加氢的车载储氢瓶参数见表1,模型输入参数见表2。
Dynamic Simulation and Energy Comsuption Analysis of 70 MPa Hydrogen Refueling Station
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摘要:
目的 加氢站是氢燃料电池车推广应用的关键基础设施。70 MPa加氢可以显著提升氢燃料电池车的续航能力和经济性。为准确分析70 MPa加氢站的能耗,降低运营成本。 方法 建立了70 MPa加氢站加氢过程动态热力学模型,基于SAE J2601加注协议研究了单次加氢过程中压力和温度的动态变化规律,分析了单次加氢的能耗组成和多次加氢的能耗变化。 结果 结果表明:单次加氢过程中165 s加满车载储氢瓶,295 s完成高压储氢瓶补氢,5 min内完成一次加氢循环。加氢能耗由压缩机、冷水机组和冷冻机组能耗组成,其中压缩机能耗超过64%,冷水机组能耗约为压缩机能耗三分之一。随着加氢次数增多,单次加氢能耗升高,第一次和第二十次加氢的比能耗分别为0.98 kWh/kg和1.24 kWh/kg。 结论 缩短单次加氢时间可以从提升压缩机流量入手。降低压缩机能耗是加氢过程节能的关键环节。三级高压储氢瓶的压力配置影响加氢能耗中的多个环节,如何对三级压力进行合理配置,值得进一步研究。 Abstract:Introduction Hydrogen refueling station is the key infrastructure for the promotion of hydrogen fuel cell vehicles. 70 MPa hydrogen refueling can significantly improve the endurance and economy of hydrogen fuel cell vehicles. This paper aims to accurately analyze the energy consumption and reduce the operating cost of 70 MPa hydrogen refueling station. Method The dynamic thermodynamic model of the hydrogen refueling process was established for the 70 MPa hydrogen refueling station. The law of dynamic pressure and temperature change during single hydrogen refueling process was studied based on the SAE J2601 refueling protocol. The energy consumption composition of single hydrogen refueling, and the energy consumption change of multiple times of hydrogen refueling were analyzed. Result The results show that during single hydrogen refueling process, the onboard hydrogen storage cyclinder is refueled in 165 s, the high-pressure hydrogen storage cyclinder is refilled in 295 s, and one hydrogen refueling cycle is completed within 5 min. The energy consumption of hydrogen refueling comes from compressor, intercooler and precooler, among which the energy consumption of the compressor is more than 64%, and the energy consumption of the intercooler is about one third of that of the compressor. The specific energy consumption during single hydrogen refueling process increases from 0.98 kWh/kg to 1.24 kWh/kg as the number of times of hydrogen refueling increases from the first to the twentieth. Conclusion The time of single hydrogen refueling process can be shortened by increasing the compressor flow rate. Reducing compressor energy consumption is the key to save energy in hydrogen refueling process. The pressure configuration of the three-stage high-pressure hydrogen storage cyclinder affects many parts of energy consumption. How to allocate the three-stage pressure is worth further study. -
Key words:
- hydrogen refueling station /
- dynamic simulation /
- energy comsuption /
- compression /
- intercooling /
- precooling
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表 1 车载储氢瓶加氢前后参数
Tab. 1. Parameters of onboard hydrogen storage cylinder before and after refueling
参数 水容积/L 温度/℃ 压力/MPa 氢气质量/kg 加氢前 141 10 10 1.14 加氢后 141 10 70 5.74 -
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