Nanjing Kesen Kenen Environment & Energy Co., Ltd (NKK), China, has recently conducted a successful engineering procurement and construction project to build a waste heat recovery (WHR) power plant at Sharjah Cement Factory (SCF) in the UAE. NKK completed the installation of the plant on SCF's two production lines in association with UAE-based subcontractor Petron Emirates Cont & Mfg Co LLC in the first quarter of 2015.
In 2012 Nanjing Kesen Kenen Environment & Energy Co. Ltd. (NKK) was informed that Sharjah Cement Factory (SCF) intended to install a waste heat recovery (WHR) system at its plant in Sharjah, UAE. NKK sent its engineers to the site twice to communicate with the owner and take measurements of the kilns.
In July 2013, the owner travelled abroad to investigate the potential EPC candidates. It saw NKK's technology and reference projects as part of this process. NKK was the only Chinese WHR supplier on the shortlist, along with one European provider and one Indian supplier. NKK's strong references meant that it was awarded the EPC contract by SCF.
WHR specifications
During the initial stages of this project, measurements taken by NKK engineers at SCF (See Tables 1-3) formed the basis of the WHR design.
Line 1 | Line 2 | |||
Clinker production (t/day) | 2233 | 4102 | ||
Item | Pre-heater outlet | Cooler outlet | Pre-heater outlet | Cooler outlet |
FG flow rate (Nm3/hr) | 150,000 | 105,000 | 280,000 | 121,000 |
Temp. at boiler inlet (°C) | 330 | 300 | 340 | 360 |
FG dustiness (g/Nm3) | 100 | 50 | 100 | 50 |
Above - Table 1: Flue gas parameters.
Source | Well |
Hardness (mg/L) | 400 - 500 |
Conductivity @25°C (mS/cm) | 6 - 7 |
pH @25°C | 7.5 |
Chlorides (mg/L) | 1700 - 1900 |
Chemical oxygen demand (mg/L) | 125 - 170mg/L |
Above - Table 2: Raw water parameters.
Item | Value |
Power distribution mid voltage | AC, 6.3kV, 50Hz, 3-phase, 31.5kA, 3s |
Power distribution low voltage | AC, 400V, 50Hz, 3-phase (4 lines) Neutral solidly grounded; 50kA, 1s |
Rated high voltage | 6.3kV ±10% |
Rated low voltage | 400V ±10% |
Frequency | 50Hz ±2% |
Rated control voltage | 110V AC for motor control centre 24V DC for distributed control system |
Above - Table 3: Power supply parameters.
System process
The system designed for this project included two air-quenching chamber (AQC) boilers, two pre-heater (PH) boilers, one turbine (rated 9MW), one generator (rated 10MW), three air-cooler condenser (ACC) units, electrical equipment, automation control system and auxiliaries. Four key design features are as followed:
- The four boilers are all with dual pressure (high pressure (HP) 1.37MPa and low pressure (LP) 0.2MPa). The turbine works with supplementary LP steam. The dual-pressure system maximises the use of waste heat and provides approximately 5% more power than a single-pressure system.
- Due to the geographical location of the site, ACC units were used to reduce water consumption compared with water-cooling condensers. This also accelerated the construction process.
- The cooling water for boiler sampling and turbo generator rotating equipment was designed as a closed circuit with an auxiliary cooling tower and make-up water tank. This also reduces water
- consumption.
- Considering that the available raw water at the site has a high mineral content, a two-stage reverse osmosis system was designed for the boiler water treatment plant. On-line sample water analysis systems are used to monitor the water quality and ensure the long-term safe operation of the boilers.
Equipment selection
Equipment | Manufacturer |
Boiler | Hangzhou Boiler Group |
Turbine | Qingdao Jieneng Steam Turbine Group |
ACC | GEA China |
Generator | Nanyang Explosion Protection Group |
High voltage panel | ABB China |
Low voltage panel | Siemens China |
Distributed control system | ABB China |
Auxiliaries | Chinese makes |
Above - Table 4: Sources of the main pieces of equipment for the SCF WHR project.
NKK's patented AQC boiler is designed with an internal dust collecting hopper, which saves on the cost of an external dust collector. The hot air from the cooler goes into the bottom of the boiler inlet and collects the clinker dust in a hopper. Heat is exchanged via bundles of tubes and used gas is exhausted from an outlet at the top. Anti-abrasion and guiding measurements are installed in order to maximise the service life of the boiler.
The PH boiler inlet tapping was installed after the high temperature (HT) fan and the raw meal inlet. The PH boiler on Line 2 has a typical design, in which the flue gas goes from the top to the bottom. To prevent ash accumulation on heat exchange tubes, a hammering system was used for the PH boilers.
Due to restricted space under the pre-heater and insufficient draft pressure at the bag-filter side, the PH boiler on Line 1 is designed in such a way that the flue gas goes into the boiler from an inlet at the bottom. It takes a U-turn at the top of the boiler and is exhausted from an outlet at the bottom, which is fitted with a booster fan. This boiler with the reversed U-shape flue gas routing is the first such reference for a PH
WHR boiler anywhere in the world.
The turbine selected for this project is a single cylinder, direct air-cooled condensing turbine including casing, bearing, housing, rotor, seals, exhaust chamber, safety and governing control system, oil system and drainage system.
The ACC used in this project is the latest design from GEA with vertical delta-shape units. The erection quality directly affects the vacuum lever during operation and consequently the power generation. The generator provided for this project is a box-type all-in-one generator with parameters as provided in Table 5 (overleaf).
Item / Parameter | Value |
Rated capacity (kW) | 10,000 |
Rated voltage (kV) | 6.3 |
Rated frequency (Hz) | 50 |
Rated speed (rpm) | 3000 |
Exciter | Brushless excitation system |
Number of phases | 3 |
Above - Table 5: Key generator data.
Installation milestones
The hydrotests and distribution commissioning for Line 1 and Line 2 were conducted in November 2014, with alkali cleaning and steam blowing conducted in December 2014 on Line 1 and January 2015 on Line 2. Synchronisation was carried out on 8 January 2015 on Line 1 and on 7 February 2015 on Line 2.
Typical problem in installation and solution
During the erection of the AQC boiler on Line 2, the piping from LP superheater header to LP superheater outlet header collided with the downcomer from the HP drum to the HP evaporator inlet header. The project manager from NKK requested that the boiler supplier remanufacture the piece.
Another problem was that the bolt holes of the feed water pump base plate were misaligned. The direction of the feed water pump outlet was different from the design, so the site team from NKK had to not only reconstruct the civil foundations, but also modify the layout of the feed water piping and adjust the alignment of the pumps.
Performance
On 23 March 2015 the performance guarantee test was carried out by NKK and witnessed by the owner. The test was completed to the satisfaction of the owner, with performance parameters as shown in Table 6.
Guarantee value | Test result | |
Duration of test (hr) | 24 | 24 |
Ambient temperature (⁰C) | 27.00 | 28.89 |
Gross power output (kW) | 8500 | 8742 |
Power consumed by auxiliary tasks / equipment (%) | 12.50 | 7.48 |
Net power output (kW) | 7437.50 | 8088.09 |
Above - Table 6: Performance test results from March 2015.
The power generated is around 350kW more than guaranteed after consideration of the ambient temperature. The Provisional Acceptance Certificate was accordingly issued by SCF to NKK.