摘 要

生物甲烷过程能够将低劣生物质转化为清洁能源，同时能够减少环境污染和温室气体效应，且生物甲烷路线更具有减排潜力，发展生物甲烷过程应对了我国能源、环境的双重需求。在影响厌氧发酵过程众多因素中，温度为关键影响因素，作为唯一可操作的变量，达到并保持合适的发酵温度是厌氧发酵工程提高产气量和有机废弃物降解速率主要方法，而我国沼气工程同国外先进水平(以瑞典为例)相比差距巨大，其主要原因在于我国的国情使得沼气工程不可能接入供热管网以保证其系统热平衡，且未建立以高效换热器为热平衡中心的换热系统。

对于我国沼气普遍存在的产气速率低，发酵效率低和能耗高的问题，可通过建立以高效换热器为热平衡中心的热利用系统，而由于沼期工程存在能耗高的问题，这就决定了必须从有源强化换热技术出发，研究适合沼气工程的强化换热结构。

本文从强化换热的角度，提出提高生物甲烷过程产气率和降低能耗的方法，试图确定在SSHE中影响热量转换的因素，并确定其重要性为了促进SSHE在各种应用中的使用。这些类型的换热器是用于高粘度的、温度变化敏感的和高亲和力的冷/热流体的沉积。对于换热器而言，流体进入换热器的速度、转子的转速、形状、叶片的数目以及施加的磁通（固定的或变化的）都是关于热转换效率方面需要调查的因素。在广泛的回顾以前的作品后，为了进一步详细阐述SSHE的性能，在冷却模式下进行了多次的研究。研究发现，在众多参数中，转子的转速是影响最大的一个，它增强了RPM值即提高了SSHE的热转换效率。

关键词：沼液换热；有源强化；刮板式换热器；场协同；强化换热

ABSTRACT

Biological methane process is inferior to process of turning biomass into clean energy. At the same time, it can reduce the environmental pollution and greenhouse effect. And the biological methane route has more potential to reduce emissions compared with other CCS route. The development of biological methane process will meet the requirements both from the demand of energy and environment in our country. Among numerous factors that influence the anaerobic fermentation process, the temperature is the key factor. As the only operational variable, to achieve and maintain appropriate fermentation temperature is the main method to improve gas production and organic waste degradation rate in biogas plants. It cannot be denied that there is huge gap in developmental level of the biogas project between China and some foreign advanced country (Sweden’s, for example). The main reason is that China's national conditions make biogas engineering could not have access to the heating pipe network to ensure heat balance of the system.What’s more, heat exchange system has not been established , which is centered on high efficiency heat exchanger.

For low gas production velocity, low efficiency of fermentation and high energy consumption of biogas plant, which are widespread phenomenons among biogas plant in our country, high efficiency heat exchanger can be built as the center of the heat balance system of the heat utilization. At the same time, considering the existing problem of high energy consumption, it is determined that the passive strengthening heat transfer technology should be the first choice to carry out the research of strengthening heat transfer structure for anaerobic fermentation process.

In order to overcome its low gas production rate and the problem of high energy consumption, this article put forward to improve biological process of methane gas rate. This study is an attempt to identify the factors influencing heat transfer in a Surface Scraped Heat Exchanger (SSHE) and determining its significance in order to facilitate the use of SSHE in various applications.These types of exchangers are employed to heat/cool fluids with high viscosity, sensitive to temperature variations and high affinity for deposition. The rate of the fluid entering the exchanger, revolution velocity of the rotor, shape and the number of blades, and mechanism of applying flux (fixed or variable) to the exchanger are the factors their heat transfer aspects investigated. After a comprehensive review of previous works, as a noble mode of elaborating SSHE, the exchanger is studied numerically to reveal its performance in cooling mode. It is found that, amongst the parameters studied, the revolution velocity of rotor is the most effective one and increasing the RPM improves the SSHE heat transfer performance significantly.

KEY WORDS: Heat Exchange of Slurry; Active reinforcement; Surface Scraped Heat Exchanger; Field Synergy; Heat Transfer Enhancement

目 录

摘要 I

ABSTRACT II

目 录 4

第一章 文献综述 1

1.1 发展生物甲烷过程的意义 1

1.2 生物甲烷过程强化换热的意义 1

1.2.1 影响生物甲烷过程效率的关键因素 1

1.2.2 生物甲烷过程的换热需求 2

1.3 强化换热技术现状 3

1.4 课题来源与研究内容 8

第二章 流场计算理论与方法 10

2.1流场计算 10

2.1.1控制方程 10

2.1.2 Fluent®中的湍流模型 10

2.2 沼液的流动特性 12

2.2.1 非牛顿流体本构方程 12

2.2.2沼液的流变性 13

2.2.3 沼液流动模拟方法的实验验证 15

第三章2D刮板式换热器 18

3.1 2D刮板式换热器CFD实验重复 18

3.1.1 刮板式换热器的参数 18

3.1.2 模拟结果与分析 19

3.2 2D刮板式换热器的拓展研究 21

3.2.1不同粘度的流体的换热研究 21

3.2.2 不同刀尖与壁面间距的换热研究 22

第四章 3D刮板式换热器 24

4.1 3D刮板式换热器的构建 24

4.2 3D刮板式换热器的换热模拟 25

4.3 管式换热器的数据研究 27

4.4 SSHE与管式换热器的对比 28

第五章 全文总结与展望 30

5.1 全文总结 30

5.2 展望 30

参考文献 31

致谢 33

文献综述

1.1 发展生物甲烷过程的意义

能源关系着国家的安全，而我国缺油少气，目前采用的解决方案就是能源外交。同时碳减排压力与日俱增，而CCS路线成本高。虽然生物甲烷过程并未发展成熟，但是刘畅^[1]等从经济技术角度对比了生物甲烷路线和CCS路线，发现前者理论捕集CO₂能耗仅为后者的一般，因而生物甲烷路线更具减排潜力。

在能源和环境的双重压力下，采用新技术生产的生物气、燃料乙醇、生物柴油等新能源将有望占全球总能耗的40%以上^[2]。我国每年产生大量低劣生物质，若能将其转化，将极大程度缓解我国天然气短缺和环境污染问题。且以生物甲烷为代表的生物质更是具有存储性，兼具资源和能源双重特性，因此利用有机垃圾做生物甲烷兼具了节能、减排和资源化的三重战略，但是我们不能不面对的问题是，生物产甲烷过程的产气率低、能耗高和系统复杂，这将是我们必须设法解决的巨大难点^[3]。

1.2 生物甲烷过程强化换热的意义

1.2.1 影响生物甲烷过程效率的关键因素

影响过程产气率的因素主要有进料中C、N、P和其他微量元素的配比、发酵过程pH值、发酵过程的混合程度和发酵温度^[4,5]。其中温度是作为可操变量且对甲烷菌的生长速率影响较大的一个，如下图1-1所示，在各个温度段中均有一个细菌活性最高的温度点，且温度越高，细菌的最高活性 ，而甲烷活性高即意味着由甲烷菌参与的厌氧发酵过程的产气能力越强。

相关图片展示：