Abstract: Currently, there is an increasing number of self-owned power plant projects outside the power system. Given the differences in design requirements between external power plants and internal power plants, this article focuses on the Dongguan Hailong Paper Co., Ltd. #5 unit project as an example, detailing specific design aspects and offering several insights. —Reflections Inspired by the Engineering Design of Nine Dragons Paper In recent years, with the deepening of reform and opening up, the level of national economic development has continuously improved. Economic development requires electricity as a priority. To meet the development requirements of enterprises, many industries have built or expanded their self-owned power plants, and with the increase in enterprise scale, the capacity of power plant units is also expanding. The construction of enterprise self-owned power plants has brought opportunities to the power design market. This allows power engineering designers more opportunities and conditions to fully engage with industries outside the power system. In recent years, our institute has undertaken the design of many new construction, renovation, and expansion projects of self-owned power plants in industries outside the power system, such as coal mines, petrochemicals, and papermaking. Because each industry has its own characteristics and different requirements for power plant operation, how to do a good job in design is a problem that every designer will face. This article discusses some experiences based on the specific design of the #5 unit project of Dongguan Hailong Paper Industry Co., Ltd. I. Project Introduction The #5 unit of Dongguan Hailong Paper Industry Co., Ltd. is part of the self-owned power plant units of Dongguan Jiulong Paper Industry Co., Ltd., a wholly foreign-owned enterprise. The planned capacity is 3×50MW coal-fired desulfurized steam extraction heating units, with busbar operation. One unit was constructed in this phase, with the public system designed according to the planned capacity. The boiler is a WGZ280/9.8-1 type high-temperature and high-pressure, natural circulation, coal-fired solid ash discharge boiler manufactured by Wuhan Boiler Factory, with an all-steel structure and open-air layout. Light oil ignition and combustion are used, and the oil gun adopts mechanical atomization. The steam turbine is a C50-8.83/0.648 type 50MW single-extraction condensing steam turbine manufactured by Nanjing Steam Turbine Generator Factory, with an electro-hydraulic regulating system. The generator is a QF-60-2-10.5 type air-cooled 60MW steam turbine generator manufactured by Nanjing Steam Turbine Generator Factory. It features a brushless excitation system. The ball mill intermediate storage type hot air pulverized coal feeding system is used, with each boiler equipped with 2 cylindrical ball mills, 2 belt feeders, 2 pulverizers, and 12 impeller feeders. The feeders and pulverizers use variable frequency speed control. The balanced ventilation system has 2 distribution fans and 2 induced draft fans per boiler, all centrifugal fans, and the air preheater is tubular. The regenerative system is equipped with 3 low-pressure heaters, 2 high-pressure heaters, 1 deaerator, 1 steam seal heater, and 1 bubbling deaerator. The utility system is equipped with 2 desuperheaters and pressure reducers. This phase of the project provides 0.648MPa, 227℃, 150t/h low-pressure steam to the newly built paper mill; the electricity is for self-use and not connected to the local power grid. II. Detailed Design 1. The control method was determined because the planned capacity of this project is 3×50MW units, with the main steam and feedwater systems connected by a common pipe. Based on the actual project situation, during the design phase, in coordination with related disciplines such as thermal power, a centralized control system for the boilers, turbines, and electrical systems was determined, with the control room adopting a three-machine-one-controller configuration. The control room was initially located between boiler #5 of the current phase and boiler #6 of the next phase. This layout was deemed reasonable and feasible, and several control room layout schemes were designed and recommended to the owner. However, after reviewing the scheme, the owner pointed out that while the three-machine-one-controller configuration was reasonable, only one unit was being built in this phase, and the construction dates for the other two units were still uncertain. From a private enterprise perspective, they did not want to sacrifice significant costs and space for the next phase, resulting in no profit and idle funds. Therefore, they insisted on using the one-machine-one-controller configuration, preferring to rebuild the control room when the next phase of the project commences. Regarding our point that the common pipe operation mode involves cross-operation of turbines and boilers between different units, the one-machine-one-controller configuration would be detrimental to the coordinated control of the three units. The owner believed this problem could be solved by increasing the workload of operators by frequently exchanging information between the three control rooms. Furthermore, the current phase of the project, with its boiler and turbine matching, could be temporarily operated using a unit-based control system to ensure safe unit operation. At the owner's insistence, we met their requirements and ultimately determined the control method to be centralized control of the boiler, turbine, and electrical systems, with each control room controlling one machine. The main electrical control building was eliminated; the boiler, turbine, generator, deaerator feedwater, desuperheating and pressure reducing, fire pumps, and circulating water pumps were centralized in one control room for unified monitoring, facilitating plant-wide operation and management. The central control room is located between columns #4 and #6 of the BC frame on the operating floor. The electronic equipment rooms are divided into two: #1 and #2. The #1 electronic equipment room is adjacent to the central control room, located between columns #3 and #4. All DCS and related cabinets are located here, and the engineering workstation is located in the #1 electronic equipment room. The #2 electronic equipment room is located between the two boilers on the operating floor, housing power distribution cabinets, thermal distribution boxes, and other secondary electrical equipment. 2. The determination of the control level is crucial to the operation and management of a power plant, determining its efficiency and effectiveness. Engineering design should first fully consider and respect the owner's opinions, but not blindly follow them. We must comprehensively consider and evaluate from a design perspective to create a finished product that satisfies the owner. The final determination of the control level for this project went through a rather tortuous process. During the scheme determination stage, the owner explicitly stated in the meeting minutes that this project would adopt a conventional instrument panel control method. We were quite surprised by this. Today, with the rapid development of computer technology, the maturity of control theory, and the updating of control methods, DCS has greatly improved in terms of safety, reliability, and practicality. With the successful application of DCS in various power plants across the country, the level of power plant automation control has been fundamentally improved, and DCS distributed control systems have become the preferred choice for power plant design. The conventional instrument panel control method, mainly based on Type III instruments, is becoming increasingly rare in modern newly built power plants due to the development of the times and technological progress, and is being replaced by DCS. Many early power plants in China that primarily used conventional panel control have already undergone or are undergoing DCS upgrades. Nine Dragons Paper is a large-scale enterprise with abundant capital. Its paper production lines are all equipped with advanced imported equipment and employ advanced control methods. However, the low level of control at its self-owned power plant is puzzling. In the spirit of serving and being responsible to the owner, we held a special discussion with them on this issue, comparing DCS control with instrument panel control in terms of operability, reliability, stability, and economy, clarifying its advantages and rationale, and hoping the owner would listen to our opinions and change their mind. However, as a proposed solution, the owner must have their reasons, analyzed as follows: (1) Since the power plant only serves as an auxiliary workshop providing industrial steam extraction for the paper mill, it represents only a small portion of the overall investment. The upper management of the paper mill has not given it sufficient attention. During the discussion, we learned that the company's #1 to #4 units use conventional instrument panels for control. The operators are very familiar with this control method, and there have been no problems in its operation. Therefore, it is natural for this unit to adopt the existing control level. (2) Due to the nature of the enterprise, all employees are working for the boss, and any mistakes at work may lead to punishment or even dismissal. The company explicitly stipulates that steam supply must not be interrupted under any circumstances, as the paper mill's profits are calculated in minutes. Production losses due to power plant malfunctions are unbearable for any employee. Operators prefer to use their most familiar operating methods to ensure they don't make mistakes, rather than considering whether these methods are reasonable or advanced. Therefore, frontline staff, for their own benefit, strongly recommend conventional instrument panels. ⑶. In non-power system industries, the understanding of DCS in the control of self-owned power plants may be limited. When visiting different power plants to inspect DCS operation, their concern is not how economical, reasonable, and controllable the DCS control system is, but rather how many accidents have occurred, how many times the system has shut down, etc., leading to a one-sided exaggeration of malfunctions and causing doubts about the reliability of the DCS, resulting in distrust. Furthermore, training operators to operate the DCS proficiently requires a considerable amount of time, and off-the-job training contradicts the company's personnel principles. The company will inevitably recruit skilled DCS operators to replace the conventional instrument operators who will have no role to play, leading to their resistance to DCS. A lack of understanding of DCS control theory and methods can easily lead to dependence on conventional instruments, making it difficult to embrace advanced production methods. The fear of operational errors and the resulting penalties or dismissal also contribute to the resistance of specific staff towards DCS. In response to these reasons why the owner preferred conventional instrument control over DCS, we conducted in-depth and detailed communication with the owner, comparing DCS hardware and software configurations, examples of power plant safety, reliability, and ease of operation, as well as DCS investment and control room layout with conventional instrument panels. After several special discussions, the owner was finally persuaded and clearly stated that the control level of Unit #5 should be improved compared to the previous four units. The decision was made to adopt a DCS distributed control system for the unit control. However, another requirement was raised: to ensure reliable operation, a sufficient number of backup manual controls should be added to maintain normal operation in the event of a DCS crash. We also strongly oppose this decision. Since the entire system has been decided to adopt DCS control, there is absolutely no need to add sufficient backup manual controls. This stems from a lack of trust in the DCS distributed control system, a fear that problems with the DCS system will affect production, and a reliance on traditional conventional panel control theories and methods. It has been proven that DCS monitoring coverage of the unit is becoming increasingly comprehensive, and the design of the human-machine interface in the unit control room has also undergone profound changes. The conventional instrument plus hard manual monitoring mode has been eliminated, replaced by large screens, CRT operator stations, and soft manual controls. The owner's requirement to "retain some backup manual controls to maintain normal unit operation in the event of DCS system failure" has, after evaluation, several problems exist: (1) This design does not comply with Clause 12.9.4 of the "Technical Specification for Design of Thermal Power Plants" (DL 5000-2000) regarding the principle of backup manual operation. Therefore, we can only design according to this clause to ensure the necessary backup manual operation for emergency safe shutdown of the unit. ⑵. Increased control room area. For a DCS design without backup manual operation, the control room area for a 50MW unit is 16×8=128m2; for a DCS control design retaining some backup manual operation, the control room area is at least 24×8=192m2. The control room is located within the BC frame, making it cramped and narrow, inconvenient for operation. It also causes inconvenience to the overall layout of the main professional components. ⑶. Significantly increased project cost. ⑷. Lack of safety guarantee. The addition of conventional instruments increases the potential for accidents. The unit requires overall coordinated control; retaining only partial operations cannot guarantee completely safe operation of the unit in the event of DCS malfunction. In this case, only a safe shutdown can be implemented. ⑸. The operational methods were chaotic. With operators accustomed to CRT and keyboard-based operations, would they still be able to handle routine operations effectively in an emergency if a DCS malfunctioned? Our institute believes that, according to the "Major Fire Prevention Regulations" and "Twenty Countermeasures," when a DCS malfunctions, emergency shutdown and furnace stoppage can only be achieved through essential backup manual operations. Relying on partial manual operations to maintain full unit operation is virtually impossible. Both sides held differing opinions, and after several rounds of negotiation, compromises were reached. We ultimately respected and agreed to the owner's suggestion to retain necessary backup manual operations to minimize paper production losses. Based on this principle, the final control scheme was: the unit adopts a DCS distributed control system, the turbine control adopts a DEH digital electro-hydraulic control system, and the unit operates primarily via CRT and keyboard. With the cooperation of on-site personnel, the unit's start-up and shutdown, normal operation monitoring and operation, and emergency handling in case of accidents can be achieved from the control room. To ensure that the unit can maintain operation in the event of a complete DCS failure or operator station malfunction, in accordance with the owner's requirements, in addition to the backup operation means such as steam drum emergency drain valve, boiler safety valve, AC/DC lubricating oil pump, etc., which are set up on the backup panel according to the "Main Fire Regulations", the backup panel also retains backup operation means for auxiliary machines, valves, and dampers such as forced draft and induced draft fans, pulverized coal feeders, main steam feeders, and feedwater feeders. Specifically, these include: ● M/A operators for the inlet dampers of forced draft fans A and B; ● M/A operators for the inlet dampers of induced draft fans A and B; ● M/A operators for the first-stage and second-stage desuperheating water dampers on both sides; ● M/A operators for the main feedwater damper, main feedwater bypass damper, and small feedwater bypass damper; ● M/A operators for the condenser makeup water regulating damper; ● M/A operators for the #1 and #2 high-pressure heater water level dampers; ● M/A operators for the deaerator pressure and water level dampers; ● M/A operators for the #1 and #2 desuperheater/pressure reducer outlet pressure and temperature dampers; These operators should be able to bypass the control system processor and use the same power supply as the control drive unit. Switching should be bidirectional and uninterrupted. In addition, the control panel is equipped with thermal signal indicator boards, furnace flame television, water level television, and related secondary instruments. The ash removal system adopts PLC+CRT control, while the chemical water treatment, fuel oil pump room, and slag removal control use conventional instruments. The auxiliary systems are housed in a workshop control room. After several changes in the owner's requirements for unit control level—from conventional instrument panels to DCS plus conventional instrument panels—and several changes regarding the use of large screens, whether one large screen per unit, or one per boiler; and the number of backup manual control units for the electrical system, we designed as many as 11 centralized control room layout schemes, ultimately achieving the owner's satisfaction. 3. DCS Functions: ● Data Acquisition System (DAS) ● Analog Control System (MCS) ● Furnace Safety Monitoring System (FSSS) ● Sequential Control System (SCS) ● Electrical Control System (ECS) In addition, it has the function of communicating with the DEH to realize the DEH operator station and to monitor other control systems (with data communication interfaces). III. Existing Problems : 1. The soot blowing system and the fixed exhaust system are not integrated into the DCS. When determining the three main units and signing the technical agreement, the owner decided to use PLC programmable control for the soot blowing system and the fixed exhaust system. Given the powerful functions and advanced operation of DCS systems, integrating soot blowing and fixed discharge into the DCS system for overall control is both reasonable and economical. Because these systems are controlled separately and operated via programmable control panels, they are not only outdated but also increase equipment investment. 2. Too many equipment selections and complex design: The owner used multiple products for the same type of equipment, such as Rotork, German PS series, and domestically produced products using French Bernard technology for electric actuators; the backup panel contained numerous different types of conventional instruments, etc. This excessive number of equipment models increased the complexity of design, installation, commissioning, and operation. 3. Inconsistent quality of winning bidders: Some manufacturers even lacked experience in power systems and power plant equipment operation, making cooperation with them during the design process extremely difficult. IV. Some Lessons Learned Through the entire design process of the Hailong Paper Industry project, I have gained the following insights, which I believe will be helpful for the design of similar projects in the future. 1. Communicate frequently with the owner. 1. The first step in completing an engineering design is to communicate effectively with the client and understand their perspectives, especially for industries outside the power system. We may lack knowledge of their unique technological requirements and operating conditions; only through thorough communication can we understand their industry characteristics and design a finished product that meets their needs. 2. Be prepared for unforeseen changes. Because the industries represented by clients may differ in their business, management, and operational characteristics, changes are possible at any time, requiring designers to revise the original design, sometimes even repeatedly. This often occurs in the early stages of a project. Designers should fully understand and support this. 3. Be responsible to the client and design high-quality projects. As a design institute, designing high-quality projects and being responsible to the client is our duty. We have a responsibility to recommend better design concepts and control theories to them, ensuring their understanding and acceptance. Only in this way can a win-win situation be achieved.