John Thompson’s Industrial Watertube Boiler business unit, despite stiff competition from Indian boiler manufacturers and difficulties caused by the worldwide Covid-19 pandemic, has succeeded in securing a new watertube boiler order for Universal Robina Corporation’s (URC) Sonedco sugar mill in the Philippines.
The Philippines is the second largest sugar producer among the Association of Southeast Asian Nations countries. URC is one of the largest sugar companies in the Philippines, operating a total of six sugar mills there.
General arrangement drawing of new 80 tph bagasse boiler for URC.
The order for the 80tph capacity boiler, awarded in September this year and due for completion in January 2022, is a strategic breakthrough for John Thompson in South East Asia.
“Negotiations were tough, but through constant price optimisation, a competitively priced, reliable and world class quality John Thompson boiler was brought to the table, securing the order,” said Lauren Barnard, Design & Applications Engineer at John Thompson’s Industrial Watertube Boilers unit in Durban.
The boiler is a girth-supported bi-drum watertube boiler and will burn mill bagasse with its combustion equipment comprising a stationary pinhole grate, three-drum feeders and pneumatic spreaders. The final steam conditions are 32bar(g), 400°C, with steam temperature control achieved via a two-stage superheater configuration with interstage spray attemperation.
“The boiler will be unique in the sense that it incorporates a number of innovative features which contribute to the unit’s high efficiency and reliability, at the same time reducing cost by adopting a value engineering approach to every aspect of the boiler,” Lauren commented.
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Inventor model of boiler pressure part arrangement.
The innovative features include:
l First new watertube boiler to be supplied into the Philippines.
l Furnace sizing and panel wall configuration is non-standard in order to fit in a higher number of fuel feeders for reliability, while keeping the width of the boiler as small as possible. The fuel feeders will be custom designed to fit the narrow width of the boiler.
l First bi-drum watertube boiler with furnace tubes of 63.5mm OD pitched at 90mm, as per the John Thompson Microgen configuration. This higher fin-to-tube ratio results in a lighter pressure part component.
l High efficiency heat recovery tower incorporating an airheater-economiser-airheater arrangement. The final airheater makes it possible to achieve a very high boiler efficiency far more economically compared to an economiser.
l Novel system employed to elevate airheater tube metal temperatures to avoid cold-end corrosion.
l Advanced over-fire air system developed by the Industrial Watertube Boiler unit’s R&D department.
l Dry ash collection on all throw out hoppers for reduced effluent loading.
l Fixed vane scrubber gas clean-up plant with modular turn down capability.
l Simplified desuperheater (based on superior feedwater quality provided by the customer).
l Optimised value-for-money offering.
“Based on successful implementation and testing at a local sugar mill in KwaZulu-Natal, the boiler will be supplied with a novel hot overfire air system, which has proven to improve combustion and ignition of the fuel – a big advantage when burning high moisture fuels like bagasse and other fibrous biomass,” said Lauren.
The innovative airheater-economiser-airheater arrangement in the heat recovery tower provides significant advantages.
“The airheaters are linked on the air side in a counterflow arrangement, thereby resulting in high undergrate air temperatures for efficient and stable combustion of wet bagasse, as well as a low final gas temperature to maximise boiler efficiency,” Lauren explained.
Fly ash disposal will be via a dry system with the boiler ash drop-out hoppers custom profiled to facilitate ash flow to the discharge points fitted with motorised double flap valves to maintain a gas-tight seal.
Emissions will be controlled using twin fixed vane wet scrubbers, allowing for turn down to 50% load. “The scrubbers will include a recycle system which recirculates the majority of the scrubber water, which will – together with the dry disposal system on the rest of the boiler – considerably reduce the load on the client’s existing ash water clarification system,” Lauren commented.
The furnace tubing and frame size configuration and fuel feeder pitching are specially customised to reduce cost.
John Thompson had to take a critical look at every component and aspect of the standard watertube boiler product in order to reduce costs and ensure its product remained competitive in the face of stiff competition from Indian and Chinese boiler manufacturers.
“As examples of the lengths we went to reduce costs, we have designed our own steam silencers, which were previously expensive, bought out items and optimised the superheater interstage header arrangement and auto-vent system,” Lauren remarked.
Proprietary John Thompson components such as the boiler pressure parts and combustion equipment will be manufactured in the John Thompson Bellville Works, while non-intellectual property components, such as ducting and steelwork, will be fabricated in the Philippines or neighbouring countries, to get the benefit of lower fabrication rates as well as reduced shipping costs.
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