The issue of not having a suitable single main blower for your ultra large sulphuric acid plants available is no longer an issue.
Suitable drives, either conventional electric motors at fix speed or variable frequency drive (VFD) systems and multi-stage steam turbines, are available in the required power range and do already operate blowers with drive powers in the 9 MW range.
With the growing plant capacities, the drive powers have continuously grown as the drive power is proportional to the handled flow rate/plant capacity. For ultra large acid plants in single blower arrangement drive powers over 10 MW will apply.
Especially in remote locations, the starting of large electric motors already is an issue that needs to be addressed at an early engineering stage. Depending on the specific electric site conditions and operating conditions, the optimum solution is to be determined on a case-by-case basis. This is done based on various control methods (IGV control versus speed control) and drive options.
Inrush currents on fixed speed motors can be successfully reduced by special designed motors, auxiliary starting methods (i.e. autotransformer) down to wound round motors with liquid starter. VFDs offer both low starting currents and potential savings during operation via speed control. The same applies to steam turbines as a driver. Due to most of the ultra large plants being sulphur burning plants with excessive heat recovery and steam production, the direct use of steam as a drive medium seems to be a preferred option.
In addition to the previously discussed trends affecting sulphuric acid plants, today they are also facing continuously rising energy costs. The main blower is by far the largest consumer of electric energy; on average 10% of energy costs are associated to the operation of the main blower. Therefore, the plant operational costs are in direct correlation to the main blower’s efficiency.
In order to support the plant’s operations in their quest for lower power consumption, the blower manufactures have focused on continuous improvements to the blower efficiency level. Through the years, substantial improvements on the blower efficiency levels have been achieved by various improvements on the aerodynamics and mechanical layout of the blowers.
Depending on the size of the blower today, state-of-the-art manufactures offer up to 90% inner efficiency and up to 87% compressor coupling efficiency. When compared to standard equipment, this is substantial savings of 5%-10%.
The combination of the continuous long-term operation of the blower with the high level power demand, the result is substantial energy savings. In times of high energy costs it should be a routine procedure for new investments to evaluate the total costs, both investment and operating, in the engineering /procurement phase. This allows customers to determine the most cost effective solution in the long run.
The blower suppliers are prepared to offer the best blower selection and optimized control methods during the project proposal phase.
By replacing existing units with state-of-the-art equipment per blower, customers could see an energy savings of more than 11% with a 4% production increase with the existing motors.
Especially in combination with revamps and plant debottlenecking, the use of high-efficient equipment should be checked to improve the overall competiveness of the plant and ensure there is a reduction in high energy costs.
With the launching of the SF 22, Howden has been able to fill a need that was previously unmet by the industry – a single blower arrangement for large sulphuric acid plants in the range of 4000 to 6000 MTPD.
This enables the plant designers to use the preferred single blower arrangement, in order to achieve lower investment costs a simpler arrangement and improved operations. Together with the high efficiency blower series and optimized control and drive options, the most efficient operation can be achieved as a counter-measure to the ever rising energy costs.