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Oily Sludge Reduction Treatment Process for Offshore Platforms


The horizontal screw filter press has the characteristics of simple structure, stable operation, low operating cost, and easy maintenance and management. Based on the horizontal screw filter press, a complete set of mechanical equipment for concentration treatment technology with biological treatment process as the core has been developed and initially used on offshore platforms.

Sludge concentration treatment technology of horizontal screw filter press

The sludge concentration treatment technology of the horizontal screw filter press mainly includes the following 4 unit modules, namely the dosing box and the auxiliary system for dosing, the dosing pump and the auxiliary system, the feeding pump and the auxiliary system, the sludge dewatering skid and the auxiliary system, As shown in Figure 1.


Sludge thickening skid unit module

2.1 Dosing Box and Dosing Auxiliary System

The composition of oily sludge is extremely complex, and it has the characteristics of sufficient emulsification, high viscosity, and difficulty in dehydration. At the same time, it is also fully considered that the offshore platform is in the surrounding environment of high salt spray and high humidity.

Therefore, the material of the dosing box is 316L stainless steel, the dimensions of the dosing box are 1.2m (length) × 1.1m (width) × 1.2m (height), and the volume of the dosing box is 1m3; the connecting flange adopts the standard ASMEB16.5, the design condition is 2.7kPa(G)/60℃, and the operating condition is ATM/AMB.

The magnetic flap liquid level gauge displays the liquid level in real-time. At the same time, it is equipped with a low-liquid level switch. The opening position of the tank is 300mm. In order to maintain a good connection with the dosing system on the platform, the dosing box adopts the quick connector method.

The interface codes of the dosing box are marked as N1 (overflow), N2 (empty), N3 (inlet), N4 (outlet), N5 (discharge), K1AB (magnetic flap level gauge), K2 (low-level gauge) ), MW (maintenance port); the flange is a butt welding flange, and its interface type is RF (Table 1).


2.2 Dosing pump and auxiliary system

Through process calculation, it is finally determined that the flow rate of the dosing pump is 0.075m3/h, the lift is 120m, the size of the inlet and outlet is 0.5in (1in=25.4mm), the pressure level is consistent with the interface of the dosing box, and the power of the metering pump motor is 1.5kW.

Considering that the equipment is arranged in a high-salt fog and high-humidity oil and gas workplace, the motor and other equipment are all of ExdIIBT4/IP56 protection explosion-proof grade, and the pipeline and related valves are all made of 316L stainless steel, with a design life of 20 years.

2.3 Feeding Pump and Auxiliary System

Through process calculation, it is finally determined that the feed pump flow rate is 2m3/h, the head is 20m, the inlet size is 0.5in, the outlet size is 1.5in, the pressure level is consistent with the interface of the dosing box, and the power of the centrifugal pump motor is 1.5kW.

Considering that the equipment is arranged in the oil and gas workplace with high salt fog and high humidity, the motor and other equipment are all of ExdIIBT4/IP56 protection explosion-proof grade, the valve core material is all made of 316L stainless steel, and the pipeline and valve shell are all made of Q235 cast iron galvanized anti-corrosion treatment. Its design life is 20 years.

2.4 Sludge dewatering skid and auxiliary system

The horizontal screw filter press is the core device of the entire sludge dewatering skid. In order to ensure the connection between the filter press and other skid blocks and auxiliary equipment, and to complete the orderly entry and exit of sludge and the functions of pressing and centrifuging, the basic parameters of centrifugation are as follows. :

The moisture content of the imported sludge is about 98%, and the moisture content of the outlet can reach below 80% after being treated by the horizontal screw filter press; the amount of imported sludge is 2m3/h, and the amount of sludge produced is 200kg/h; The mass fraction is 1.5‰~2‰, and the mass fraction of the chemicals in the sludge is 50×10-6~80×10-6.

The volume of the anti-static precipitation reactor is 2m3. The volume of the dosing box is 1m3 to meet the process requirements. The diameter of the drum is 250mm, the length is 1000mm, the speed is 5400r/min, the screw differential speed is 2~20r/min, and the motor power is 7.5kW+3kW+1.1kW.

Due to the technological factors of mechanical equipment manufacturing, the bearings of Japan NSK are selected.

In view of material corrosion, all parts in contact with material are made of 316L stainless steel.

The spiral blade is constantly worn during the operation of the equipment, and the pushing part of the spiral blade is made of spray-welded Gni-W2C65% wear-resistant cemented carbide with a thickness of ≥3mm.

The drive mode of the equipment is controlled by double motors and double frequency converters to increase the reliability of equipment operation, and the frequency converters use the Japanese Sanken brand. The equipment is placed indoors, the average noise is ≤85dB(A), the no-load vibration is ≤4.5mm/s, and the dry weight of a single machine is about 1t.

Offshore platform complete set

3.1 3D model skid design

The three-dimensional model skid design of the decanter filter press is based on the “safety rules for fixed offshore platforms”, and a complete set of devices has been developed that meets the installation requirements of offshore platforms and is suitable for high salt fog and high relative humidity environments.

Cable ducts and instruments and their connections should be on the same skid as the equipment.

In order to facilitate the operation and maintenance of personnel and ensure the safety of personnel, all equipment should be installed on the skid block, and no part of the equipment should be suspended beyond the edge of the skid block. For the design of the steel structure related to the base of the skid and the equipment on the skid, consideration should be given to the force that can withstand an acceleration of 1.5m/s2 in all directions.

Finally, after calculation and considering the process flow and equipment selection parameters, the three-dimensional design of the sludge dewatering skid of the compact decanter filter press is carried out, and the size of the entire skid is determined to be controlled at 3.8m (length) × 2.0m (width). ) × 2.2m (height), it includes dosing device, feeding device, decanter filter press, electric control part and equipment base.

3.2 Preliminary application of the device

The horizontal screw filter press type sludge dewatering unit is the core part of the whole pretreatment process, which presses and concentrates the oily sludge to realize the reduction treatment. The horizontal screw filter press sludge dewatering unit consists of an anti-static precipitation reaction vessel, a reciprocating screw conveyor and a set of reciprocating filter presses.

The anti-static precipitation reaction vessel is guaranteed to have a large enough volume, especially a sufficient depth, through process calculation. In order to improve the processing efficiency, a liquid level transmitter is added on the container, and there are 5 liquid level points: high, high, medium, low and low. The point is the empty tank alarm point.

The process calculation ensures the maximum utilization of the physical space of the container, and ensures the precipitation, flocculation, oxidation neutralization reaction of the liquid level and the oil absorption time of the agent.

The oily sludge after the chemical reaction has a certain lubricating effect to ensure the smoothness of the equipment during transportation. The supernatant of the anti-static precipitation reaction vessel is directly transported to the air flotation device on the offshore platform for processing, and the sludge produced by precipitation and flocculation needs to be further pressed and concentrated.

The screw part is mainly composed of differential, screw, drum, filter press, hood, machine base, lubrication system, main and auxiliary motors, etc. How it works is:

The suspension enters the drum through the feeding pipe and the spiral discharge port. Under the action of the centrifugal force generated by the high-speed rotation, the solid particles with higher density are deposited on the inner wall of the drum, and the spiral blades that move relative to the drum continue to move the drum. The solid phase particles deposited on the inner wall of the drum are scraped off and pushed out of the slag discharge port.

The separated clear liquid flows out of the drum through the opening of the weir plate, and the relative movement between the screw and the drum is realized by the differential.

The casing of the differential is connected to the drum, and the output shaft is connected to the screw.

The motor drives the rotation of the drum and also drives the rotation of the differential housing. Since the input shaft is controlled, the planetary gear is driven to drive the output shaft to rotate, and the torque is transmitted to the screw according to a certain speed ratio, so that the oily sludge contains solids. The amount of sludge is continuously increased, and the sludge is continuously extruded and dehydrated, thereby achieving the effect of preliminary pressing of oily sludge.

The water content of the oily sludge after preliminary filter press is greatly reduced, and then it is transported to the depth filter press device through a screw conveyor for final filter press dehydration. The pressure filter container is equipped with a liquid level transmitter, and the outlet pump is controlled to transport the pressure filtrate back to the anti-static precipitation reaction container. The pressed cake is released in a cake filter, bagged and shipped to land, as shown in Figure 2.


The test site is a drilling platform in the Bohai Sea. The treatment scale is 2m3/h, the sludge is about 200kg/h, and the moisture content of the sludge after treatment is reduced from 98% to below 80%. It basically meets the design requirements of the device, and the dosing concentration of the organic flocculant is 8mg/L.

After treatment, the oil content of the liquid phase is generally 500mg/L, and the solid suspension concentration is about 200mg/L, which meets the import index requirements of the air flotation treatment unit on the offshore platform.

The compact decanter filter press sludge dewatering skid has the characteristics of small footprint, simple system structure, low failure rate, low equipment operating noise and no vibration.

4 Conclusion

With the continuous progress and in-depth research of sludge treatment technology, the country’s requirements for the environmental protection industry continue to increase, and the solid waste treatment process on offshore platforms will be increasingly improved. In the future, advanced sludge dewatering technology will be used on offshore platforms. It will be inevitable.

The currently developed horizontal screw filter press is too dependent on chemicals, and it is necessary to screen reasonable types and dosages of chemicals for different sludge components, which increases the complexity and cost of equipment operation.

The direction of future efforts is how to reduce the dosage of chemicals and develop general-purpose chemicals. In terms of mechanical equipment design, we still aim at compact and small footprint, expand series of products, and develop different types of sludge dewatering process treatment devices. To suit different types of offshore work platforms.

The theoretical research on oily sludge treatment in my country started late, and there is a certain gap with developed countries in the comprehensive treatment technology and level of oily sludge. It is believed that through the continuous efforts and research of scientific researchers, sludge treatment will eventually achieve its stabilization. , reduction, harmlessness and resource utilization goals.