黎明老师最准平特肖 www.ggois.icu     發布日期：2017-01-05
Design optimization of long district heating transmission pipelines
Mikael Jakobsson, 邁克爾·雅各布遜
District heating transmission pipeline, district heating, district energy, environment friendly
Introduction to long district heating transmission pipelines
In Northern Europe long district heating transmission pipelines have been applied for decades, being a technical solution to achieve multiple benefits, including but not limited to;
Utilization of surplus heat from remote industries and power plants
Balance available heat production capacity and heat demand, by merging district heating networks
Merging district heating networks to achieve a more optimized global production mix
The distance of a “long” district heating transmission pipeline is not defined in Northern Europe, and is a relative term. The feasibility of long district heating pipelines is project specific and will highly depend on the local conditions.
In Northern Europe some district heating transmission lines ranges more than 100km. Some are connecting remote heat sources such as surplus heat from industries or power plants, while others are somewhat more complex connecting two or several individual networks.
In China district heating transmission pipelines has been applied for decades as well – often larger (in terms of pipe dimensions) than the ones that can be found in Northern Europe. As the Chinese district heating systems are developing rapidly, aiming for global energy efficiency, utilization of district heating transmission lines for the very same purposes as in Northern Europe are increasing.
在中國，集中供熱輸送管道也已經應用了數十年，通常比在北歐所用的管徑更大。 隨著中國集中供熱系統的迅速發展，以整體能源效率為目標, 與北歐一樣，集中供熱長輸管線的應用逐漸增加。
The abundant heat resources from remote power plants are being utilized in greater extent which allows heating areas to be expanded and local boilers to be demolished.
The technical- and financial feasibility of long district heating transmission lines has been widely debated. There is no single correct answer in regards to the feasibility of long district heating transmission lines, as it highly depends on the local conditions, design practice, chosen technologies, implementation, operation and maintenance etc.
Therefore, to copy a transmission line design from Northern Europe without evaluating the feasibility in the local Chinese context, is doomed to fail. Nevertheless, there are many lessons to learn from long district heating transmission line project in Northern Europe, that can be used as inspiration when developing solutions for the local conditions in China.
There are different approaches when designing district heating transmission pipelines.
The district heating transmission systems for merging networks in greater Copenhagen, VEKS and CTR, are independent systems separated from the local district heating systems with heat exchanger stations. VEKS and CTR has higher pressure- and temperature levels that the local district heating systems. The VEKS district heating transmission system is approximately 135km long and the CTR district heating transmission system is approximately 55km.
In greater Stockholm, however, most district heating transmission pipelines are directly connected with the local district heating systems and designed for the same pressure- and temperature levels. The greater Stockholm district heating system comprises several district heating transmission pipelines ranging up to approximately 80km individually.
In both Copenhagen and Stockholm, the local district heating system comprises primary and secondary networks, most often separated with building level substations. There are pros and cons with both approaches. In Stockholm the philosophy is to minimize OPEX and CAPEX, as large-scale heat exchanger stations are expensive, and will generate a temperature drop that will influence the efficiency of power plants, heat-pump facilities, flue-gas condensation etc. However, as the district heating system in greater Stockholm comprises several district heating companies, it is important that there is a well-developed cooperation model to avoid conflicts as events in one system will influence the others. This has been addressed with tailor-made planning- and operation tools, special trained operation optimization personnel, solid cooperation models, among others. In Copenhagen one of the arguments for separated systems are：clear system/ownership boundaries and that the systems can be individually designed depending on the needs. The figures below illustrate the greater Copenhagen district heating system and the greater Stockholm district heating system.
The maximum velocity in district heating transmission pipelines in Northern Europe will most often depend on a financial evaluation comparing OPEX (pump cost and heat losses) and CAPEX (pipeline investment) for different alternatives. Below, the left graph illustrates the principle of calculating annual total distribution cost. The right graph has consolidated the total cost, and added a third axis; temperature level.
北歐集中供熱輸送管網的最大流速通常取決于對不同備選方案的運行費用（泵的電耗以及熱損失）和投資成本（管線投資）的財務評估。 下圖左圖顯示了計算年總分配成本的原理。 右圖合并了總成本，并添加了第三個軸：溫度水平。
Additionally, hydraulic safety analysis is carried out in order to assure the safety of the system in case of i.e. pump maneuver or valve maneuver with the chosen maximum velocity. Noise is another factor that should be considered when deciding maximum velocity of pipelines, not least for pipes near consumers. It should also be noted that high velocities could be more critical in small dimensions, as larger pressure losses are generated than in pipes with larger dimensions.
此外，要進行水力安全分析，以確保在所選最大流速時泵調節或閥調節等工況的系統安全性。 噪聲是決定管道最大流速時應考慮的另一個因素，尤其是對用戶附近的管道。 還應當注意，在小口徑管道中的高流速可能更加值得關注，因為小管徑管道里產生的壓降比大管徑管線的壓降更大。
Hydraulic safety (transient-state) analysis
Hydraulic safety (transient-state) analysis are frequently carried out in Northern Europe to assure that the district heating systems are safe. The analysis is carried out both during design of new systems, but also for existing systems to assure that any new operation modes are safe as the systems develop continuously.
Almost any system could have potential safety issues in case of i.e. pump trips, pump maneuver or valve maneuver, but for systems with high velocities, long distances or high elevation differences the importance of carrying out hydraulic analysis is even more critical.
In Northern Europe there are standards regulating maximum allowed pressure, 6 bar(g), 10 bar(g), 16 bar(g), 25 bar(g) and so on, but there are no standards regulating minimum pressures. Too low pressure can have even greater consequences than slightly too high pressures. At a certain pressure, depending on the temperature, the water will evaporate to steam. The steam formation can move unpredictable in the pipeline until it condense back to liquid and a huge pressure peak may occur. Therefore, it is important to assure that neither too high or too low pressure occur in the system, both in normal operation and in case of any failure.
北歐有標準規定最大允許壓力，6 bar（表壓力），10 bar（表壓力），16 bar（表壓力），25 bar（表壓力）等，但沒有標準規定最小壓力。 太低的壓力相對于稍微高一些的壓力，可能會造成具有更大威脅的后果。 在一定壓力下，根據溫度情況，水會蒸發成蒸汽。 而蒸汽形成后在管線中到移動是不可預測到，在其冷凝為液體之前，都可能產生巨大的壓力峰值。 因此，確保在正常運行和任何故障的情況下系統中不出現過高或過低的壓力，至關重要！
Below a pipe that has been affected by a water hammer is illustrated (left picture) and a screenshot from the animation from the regular hydraulic transient analysis showing the transient events in Stockholm district heating system in case of pump trip (right picture).
To understand the theories behind hydraulic transient calculations, and thus understand the results and their origin, is of great importance when carrying out hydraulic safety analysis. This is not least important as hydraulic transients can be devastating, ruin assets for millions (not to say billions) due to broken pipes, compensators, heat-exchangers etc., but even worse; be a matter for personal safety as hot water can be released and harm both workers and the public. Only by understanding the source of critical hydraulic transients, feasible safe solutions can be developed and implemented – a software is only a calculation tool.
Depending on the origin and consequence of the hydraulic transient, there are many different solutions to solve such problems. The solutions could however differ a lot in terms of reliability, investment cost and operation cost. To illustrate this, an example is presented below：
水力瞬變的起因源和后果不同，則有許多不同的解決方案來解決這些問題。 然而，這些解決方案在可靠性、投資成本和運行費用方面可能存在很大差異。 為了說明這一點，下面給出一個例子：
In a fictive Chinese city with valleys, a power plant is located outside the city at a higher elevation than the city center. A district heating transmission line, with a booster pump station, is constructed to supply heat from the power plant to the city center (to the right in the picture), which is located on a lower elevation than the power plant. The hydraulic steady-state analysis presented in the picture, shows that the system is safe in normal operation. In case of pump trip in the booster pump station, there is an obvious risk that one pressure wave hits the high pressure limitation at “A”, and that another pressure wave hits the low pressure limitation (for evaporation) at “B”. Hydraulic transient analysis will show if it is likely, possible or unlikely to hit any of the pressure limitations. However, no software is able to suggest the most reliable and/or cost effective solution to potential problem. In this specific case, possible solutions to the problem could be; i) increased dimensions to reduce the velocity, ii) increased pressure rating of the pipeline system and increase the holding pressure, iii) install a heat exchanger station instead of the booster pump station, iv) change pump head in CHP and booster pump station, v) change pump arrangement to symmetric pumping in the booster pump station, vi) install pressure vessels, surge tanks, steam release valves in strategic places, vii) construct a direct connected Thermal Energy Storage tank to act as combined holding pressure and pressure separator between CHP and the district heating system, among other solutions. It can easily be realized that the cost implication between the different solutions may vary dramatically. To construct a heat exchanger station, instead of just change the pump arrangement or even just adjust pump heads, could differ with tens (not to say hundreds) of million RMB in investment. To increase pipe dimensions in order to reduce velocity, would not only increase the pipe investment, but also increase the heat losses.
假設一個山區地帶的中國城市，某發電廠位于城市之外，地勢高于市中心。在兩地之間建有安裝了中繼泵站的集中供熱長輸管線，將來自發電廠的熱量供應到海拔位置低于發電廠的市區中心（圖中右側）。圖中顯示的穩態水力分析顯示，系統在正常運行中是安全的。在中繼泵站中的泵跳閘的情況下，會有一個壓力波觸及“A”點的壓力上限，而另一個壓力波觸及“B”點的壓力下限（防止汽蝕），此風險顯而易見。動態水力分析將顯示是否有觸及任何壓力限值。然而，沒有任何軟件能夠為潛在的問題提供最可靠和/或成本效益最好的解決方案。在這種特殊情況下，解決問題的可能辦法是： i）增加尺寸以減小流速，ii）增加管道系統的壓力等級并增加定壓，iii）安裝隔壓站而不是中繼泵站，iv）在熱電聯產廠和中繼泵站中改變水泵揚程， v）將在中繼泵站中的泵布置改變為對稱設置泵組，vi）在重要位置安裝膨脹罐，緩沖罐，蒸汽釋放閥，vii）建造直接連接的蓄熱罐，既可以作為定壓點和又能作為熱電廠和集中供熱系統的壓力分離設備。不難得知，不同解決方案之間的成本投入可能差別很大。建一個熱交換器站，而不是僅僅改變泵的布置或僅調整水泵揚程，可以會有幾千（而不是幾百）萬元的投資差異。為了降低流速而增加管道尺寸，不僅會增加管道投資，還會增加熱損耗量。
This case presented above represents a relatively common district heating system in China, and illustrate some of the important matters to consider while both designing new safe systems, or implement safe solutions to existing systems. Merged district heating systems with several production sites, booster pump stations and other facilities will require more experience from the engineers carrying out the transient analysis in order to define, analyze and develop solutions for the most critical scenarios.
As a comparison the greater Stockholm merged district heating system should be mentioned, which comprise over 20 production sites, 3 different pressure levels, over 10 booster pump stations, over 100 meter elevation difference, 4 Thermal Energy Storage tanks and production costs that change on daily basis which change the operation modes and which direction the water is distributed.
Below a pressure diagram and heat load curve (inc. boiler priority) for a newly developed Chinese district heating system is illustrated, comprising 3 merged district heating networks, 2 booster pump stations, 5 production sites and 1 transmission pipeline.
Below pressure diagrams illustrates the hydraulic transient events along the pipeline route, in case of pump trip in one of the booster pump stations. The pressure diagrams are exported from the movies/animations, generated through hydraulic transient-state analysis, illustrating the entire pressure transient event in the system. First diagrams from the left illustrates the pressure levels at 0 seconds (normal operation, before pump trip). Second diagram from the left illustrates pressure levels at 5 seconds after pump trip. Third diagram from left illustrates pressure levels at 10 seconds after pump trip. Forth diagram from left illustrates pressure levels at 50 sec after pump trip.
下面的壓力圖說明了在某中繼泵站中的泵跳閘的情況下，沿著管線路線的水力動態工況。 該壓力圖從通過動態水力分析生成的電影/動畫中導出，展示了系統中的整個壓力瞬變事件。 左邊的第一個圖表顯示了0秒（正常運行，泵跳閘前）的壓力水平。 左起的第二個圖示出了在泵跳閘之后5秒的壓力水平。 左起第三個圖示出了在泵跳閘之后10秒的壓力水平。 第四張圖表說明了泵跳閘后50秒的壓力水平。
From the diagrams, it can be seen that after 10 seconds, too low pressure appears in the second pump station (third diagram form left), and that after 50 seconds too low pressure appears near the CHP (forth diagram from left).
Nordic District Heating expertise present on the Chinese market
The article is written by Mr Mikael Jakobsson, who holds a M.Sc. degree in Engineering from the Royal Institute of Technology (Sweden), and has practiced hydraulic steady-state and transient-state analysis for over 15 years. Mr Jakobsson has worked 8 years continuously on the Chinese District Heating market, and carried out over 50 projects being stationed in Beijing and Nanjing. Mr Jakobsson started his career working for Stockholm Energy (Fortum), being responsible for operation and design optimization of the greater Stockholm District Heating system. Influenced by his father, who has been engaged in District Heating management and supervision of all his life, Mr.Jakobsson started his experience even before school, and worked with his father every day around the district heating sites.
Today Mr Jakobsson holds the position as Chief Marketing Officer, as one of the international competences in the Swedish engineering consultancy company Termoekonomi.
本文作者Mikael Jakobsson先生，擁有瑞典皇家理工學院的工程學碩士學位，擁有15年以上靜態和動態水力分析經驗。 Jakobsson先生連續8年深入中國集中供熱市場，在北京和南京開展了50多個項目。 他早年在在斯德哥爾摩能源（Fortum 富騰集團）工作，負責大斯德哥爾摩地區供熱系統的運營和設計優化。而受到一輩子從事供熱工作的父親的影響，早在孩童時期，他就開始跟隨父親在供熱現場管理和監督整個集中供熱系統了。
Termoekonomi has been active in China since 2004 providing engineering consultancy services within Thermal Power, District Energy and Large-scale Heat-Pump facilities. In China Termoekonomi operates through the fully owned subsidiary Beijing Ruitengmao Energy Conservation Technology Co. Ltd (RTM). In Sweden Termoekonomi acts as a design institute, while in China Termoekonomi acts as a compliment to the local Chinese design institutes. Having an efficient organization with a combination of international and domestic specialists, localized in China, have shown to be a successful way to provide professional services timely and cost-effective.
瑞典騰茂公司（Termoekonomi AG）自2004年以來一直活躍在中國，在熱電、區域能源和大型熱泵項目中提供工程咨詢服務。 在中國，騰茂通過全資子公司北京瑞騰茂節能科技有限公司（RTM）運營。 在瑞典，騰茂是一家專業設計院，而在中國，騰茂是中國本土設計院的補充。 擁有扎根在中國的國際和國內專家的高效組織，為當地市場及時并提供高性價比的專業服務，是騰茂能夠在本地市場取得成功的主要原因。
Below the areas of special expertise, services of expertise and Termoekonomi’s value propositions are listed.
For more detailed information about the article (both in Chinese or English), if you have any needs for design optimization, operation optimization, safety analysis, general due diligence etc. of your district energy system, or if you just need some general advice; don’t hesitate to contact Mr. Mikael Jakobsson at [email protected], or China District Heating Association.