Artificial sandstone system and concrete equipment management of large hydropower stations

Brief Introduction of Equipment Management Mode of Artificial Sand and Stone System and Concrete Mixing System of Large Hydropower Stations Under Construction in China

1 artificial sandstone system equipment

1.1 Process

At present, in the artificial sandstone aggregate processing system of domestic hydropower station engineering, the production process has two crushing sections plus sand, three crushing sections plus sand, and set secondary screening, three screening, four screening, bone Material washing mud, aggregate shaping, etc.

According to the production capacity of the system, the lithology of the source, the fineness of the product, the quality of the concrete grading, and the quality of the finished product, ensure the reliable operation of the system, advanced technology, economical rationality and the advanced nature of the main equipment and their matching. After technical and economic comparison, determine System production process.

1.2 Equipment selection

The selection of various crushing equipment and sand making equipment, such as source, advantages and disadvantages, is shown in Table 1.

Example 1: The Xiaoxi sand and gravel processing system of the Three Gorges Project is the main base for the finished sand and part of the stone required for concrete pouring in the main dam of the Three Gorges Dam. The rock lithology is porphyritic granite with a small amount of diabase veins. The rock has high compressive strength and a large abrasion index. According to the design of the construction organization, the system is designed according to the peak and monthly concrete pouring of 500,000 m3 of artificial sand and 129,000 m3 of gravel in 2000. The processing scales of coarse crushing, medium crushing, fine crushing, superfine crushing and rod grinding workshop are 2400 and 1180 respectively. 1020, 1440, 200t/h, and mainly produces four-stage pre-cooled concrete aggregate. The MK-II-50-65, HP-500ST and B9100 crushing equipment used in this system are the first in China.

Example 2: The artificial sandstone system at the central site of Xiluodu Hydropower Station provides 2.8 million m3 of aggregate and aggregate required for shotcrete for diversion tunnels, flood discharge tunnels, underground powerhouse systems and other construction facilities. The source of material is diversion tunnel basalt. The compressive strength is 219 to 293 MPa. The system design wool processing capacity is 850t / h, the finished material production capacity is 700t / h, of which the artificial sand production capacity is 240t / h, its fineness modulus is 2.6 ± 0.2), the stone powder content is 10 ~ 15%, surface moisture content 6%.

1.3 related issues

(1) Stone powder recovery method: natural precipitation and drying, excavation of stone powder into the sand; negative pressure water absorption, accelerate the drying of the sedimentation pool stone powder; screw machine and high frequency vibration dewatering sieve.

(2) Requirement of RCC RCC dam for finished sand

Because RCC RCC requires a stone powder content of up to 17 ± 2%. If the wet process is used, the quality of the finished sand is good, but there is a phenomenon of loss of fine sand and finished sand, and the recovery effect is not good. The content of stone powder in the finished sand is low; if it is produced by dry process, the content of stone powder in the finished sand Meet the requirements, but the finished sand grade is not ideal (lower intermediate grade).

(3) The fineness modulus of basalt rolled artificial sand is high and the content of stone powder is not enough, especially the low content of stone powder, which has great influence on concrete workability and performance, and should be included in system design and equipment configuration. Fully considering the selection of the stone powder recovery device, it is also necessary to increase the technical research on increasing the stone powder content of the sand production equipment.

2 concrete mixing system equipment

2.1 mixing building (station)

At present, the concrete mixing building (station) used in the construction of hydropower stations in China has two types of self-propelled and forced type. The main parameter series of productivity (m3/h) are: 30, 45, 50, 60, 75, 90, 120. 150, 180, 240, 270, 320, 360. The mixer has double cone tilting self-falling type, reverse discharge self-falling type, double horizontal shaft forced type, single horizontal shaft forced type and planetary type, and its nominal capacity (L) series are: 750, 1000, 1500. 2000, 3000, 4500, 6000, 7500. The domestic mixing plant (station) is mature in technology and can meet the needs of hydropower station engineering mixing normal enthalpy, pre-cooling enthalpy and RCC roller compaction.
In order to cope with the need for rapid pouring of RCC dams in hydropower stations in recent years, the market share of self-priming or forced mixing equipment for mixing RCC, especially for forced concrete mixing plants (stations), is increasing. The domestically produced continuous concrete mixing equipment has been put into use in some medium-sized hydropower projects, but it cannot fully meet the needs of high-strength RCC production with temperature-controlled pre-cooling requirements.

At present, the latest technical status of domestic mixing building is: the main node of the mixing steel structure adopts the pin connection (shortening the installation period), and the control system adopts the dual-machine dual-control hot backup three-screen display technology (improves the reliability of the microcomputer control system); New technologies such as control, diagnosis, and troubleshooting. The main external supporting parts, such as the main control and execution components, are selected from the world-famous manufacturers with mature, reliable and cost-effective products. The mixing machine with the nominal capacity of more than 3m3 (double-shaft forced and double-cone tilting self-falling), generally Use imported products (not yet domestically produced).

In the second stage of the Three Gorges Project, five concrete mixing systems are arranged on different elevations. The normal production capacity of normal temperature concrete is 2360m3/h, and the total production capacity of pre-cooled concrete is 1870m3/h (see Table 4). The mixed concrete is directly transported to the 6 towers (tops) with 6 feeding lines to carry out the cloth into the warehouse; this new factory-made assembly line production mode, in contrast to the traditional operation mode of single-tank pouring, makes concrete The high-speed continuous pouring can be realized, which greatly improves the productivity and ensures the quality and construction period of the Three Gorges Project. From 1999 to 2001, the amount of pouring for three consecutive years was more than 4 million m3 (in 2000, the world's highest record of concrete annual pouring strength of 5.48 million m3 and monthly pouring strength of 553,000 m3 was created). From 1999 to 2004, a total of 20.55 million m3 of concrete was poured into the Three Gorges Project.

3 large-scale hydropower station sand and gravel system, mixing system equipment procurement model

3.1 crushing equipment procurement mode

The artificial sandstone system equipment is generally purchased by the contractor, but the crushing equipment, especially the sandstone system imported crushing equipment (including the stone powder recycling device) that supplies the sandstone aggregate to the main project of the hydropower station, is also purchased by the owner.

There are many manufacturers of domestic crushing equipment, such as Luoyang Dahua, Guiyang Chengzhi, Shanghai Shanbao, etc. Foreign manufacturers mainly include: US Nordberg, Astec, Finland metso, Swedish svedala, sandvik, Japanese kobelco, etc.

3.1.1 Contractor self-purchasing

The contractor selects the optimal imported crushing equipment for the bidding of the gravel system project. After winning the bid, the contractor undertakes the equipment procurement according to the commitment of the project bidding stage. The owner can provide financial support to the contractor in the form of advance payment or payment of advance payment.

For example: Yunnan Xiaowan Hydropower Station, Pubugou Hydropower Station, Sanxia Project sand and gravel system capacity increase period, Xiluodu Hydropower Station preparation period sand and gravel system.

Advantages: The contractor is responsible for purchasing equipment and the owner has less coordination.

Disadvantages: In order to minimize the investment of new equipment, the contractor often “optimizes” the sandstone system equipment after the bidding: the old generation is new, the small generation is large, and the equipment configuration is reduced, which is not conducive to engineering guarantee.

3.1.2 Owners purchase main imported crushing equipment

Under the condition that the key equipment is purchased by the owner through international bidding, the contractor uses the equipment belt scheme to bid for the sand and gravel system, responsible for system design, construction and operation.
After the bid opening, the owner purchases the imported equipment and submits it to the contractor for installation. When the project is completed, the contractor promises to repurchase the equipment according to the bidding commitment.
For example: Guangxi Longtan Hydropower Station, Yunnan Jinghui Hydropower Station, Chongqing Pengshui Hydropower Station.

Advantages: The owner can effectively control the procurement of equipment, avoiding the above-mentioned old generation and new generation.

Disadvantages: During the procurement, installation, commissioning and operation of the equipment, the owner assumes the responsibility for supply, and thus needs to invest more energy to coordinate the relationship between equipment manufacturers and contractors.

3.2 Mixing system equipment procurement mode

At present, the concrete mixing plant (station) with a nominal capacity of 3m3 or more for the mixing power plant used in the construction of the hydropower station in China is generally purchased and operated by the project owner, and is repurchased by the contractor at the end of the project. Among them, the mixing main machine with a nominal capacity of more than 3m3 (double horizontal shaft forced type and double cone tilting self-falling type), because it is not yet manufactured in China, generally adopts imported products; the mixer has a nominal capacity of less than 3m3 of mixing building (station). It is generally purchased by the contractor (the project owner provides financial support).

At present, the domestic concrete mixing plant production enterprises mainly include: Zhengzhou Hydraulic Concrete Machinery Co., Ltd., Zhengzhou Sanhe Hydraulic Machinery Co., Ltd., Guodian Machinery Design Institute, Shaanxi Construction Machinery Co., Ltd., etc. The foreign manufacturers mainly include Japan IHI, Germany. BHS, CIFA Italy, SICOMA, Italy, JOHNSON-ROSS, etc.

4 sandstone system, mixing system management mode

(1) The owner entrusts the design unit to compile the bidding documents for the gravel system and concrete mixing system, and the contractor has the general contracting method for the project bidding, responsible for geological exploration, design, equipment procurement, construction safety and operation management.

Advantages: The owner has less responsibility for system construction and operation, and less coordination work. The equipment purchase fee, depreciation fee and other expenses are included in the unit price of the finished sand and stone or the unit price of the concrete, and the residual value of the equipment is owned by the contractor. At the end of the project, the owner does not bear the pressure of equipment storage and storage and asset disposal.

Disadvantages: Due to the owner's lack of equipment procurement and system construction, there may be cases where the equipment order is not timely due to the contractor's financial problems, the arrival of the goods is delayed, or the contractor fails to purchase and configure the equipment required by the bidding documents. Reduced engineering support, so there is a certain engineering risk.

(2) The owner provides the main equipment (such as imported crushing equipment and large mixing building). The other equipment of the system is configured by the contractor. The contractor is responsible for the installation, commissioning, operation and maintenance of the system equipment, and promises to repurchase according to the bid documents after the completion of the project. Owner equipment.

Advantages: Since the main equipment is purchased by the owner, the timeliness of equipment ordering and equipment performance are within the controllable range of the owner, which is beneficial to improve the reliability of the system.

Disadvantages: The owner has a large contractual responsibility for system construction and operation due to the main supply equipment, and there are many coordination work between equipment manufacturers and installation units in the actual operation process.

5 conclusions and recommendations

At present, the production technology and equipment selection and configuration commonly used in the gravel processing system of hydropower station engineering are relatively mature, but the sand making process, such as basalt sand making, and the recycling of stone powder of RCC sand, needs further research and exploration.

In order to prevent the contractor from using the old equipment for the system equipment, the owner or the supervisor should appropriately participate in the equipment procurement work undertaken by the contractor and use the equipment that is required by the small bidder to purchase and configure the bidding documents. The owner's advantages in terms of reputation and capital help the contractor to negotiate contracts with equipment manufacturers on equipment selection, price, and after-sales service. The owner provides financial support to the contractor in the form of advance payment or payment of advance payment to ensure timely ordering and delivery of major equipment.

Open, fair and just choose a professional team with strong hydropower station sand and gravel mixing system to enter the market, in order to facilitate the construction and operation management of the sand and gravel mixing system by the owner and the supervision unit.




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