Operational Cost Reductions in a Paper Mill

A fit-for-purpose vacuum system and efficient doctoring and dewatering solutions for forming and drying sections are the fundamental base for enabling high energy efficiencies coupled with low cost pulp, paper, board and tissue production.

By Jukka Lehto, CEO & Managing Director, Jussi Lahtinen, Sales Director & Patrik Högl, Technical Sales Manager, Runtech Systems Oy

INTRODUCTION

Runtech Systems Ltd. is a privatelyowned Finnish company that develops, designs and supplies equipment to the paper, tissue and pulp mills. Hundreds of paper, tissue, board and pulp mills benefit from our dewatering meters, vacuum systems, tail threading equipment and doctoring solutions. Years of hands-on paper-making know-how differentiates Runtech from traditional hardware suppliers. Our customers benefit from integrated solutions that result in significant operational cost savings, improved machine runnability and product quality.


VACUUM USE IN A PAPER MACHINE

Vacuum usage in a paper machine is used for a variety of reasons. Dewatering the paper sheet is the obvious usage; holding and controlling the route the sheet takes through the press section and conditioning the press felts are other uses of vacuum in a paper machine. Vacuum is also used to hold and control the water jet at a suction roll.

Early paper machine designs did not use vacuum at all, but relied on gravity and press nips to dewater paper. This we refer to as nip-dewatering. Machine speeds were historically much slower than they are today. It is hard to imagine a modern paper machine without a vacuum system, and felt-dewatering is still the most common way to dewater the paper in the press section.

The vacuum levels in a paper machine are typically between 5 and 70 kPa – a relatively low figure when compared to other vacuum applications in, for instance, the chemical industry. The air flows, though, are very high due to the large open areas found in a paper machine.

Vacuum usage, which is a result of air being pulled through a restriction, is an expensive tool; it is one of the top three energy consumers in a paper mill. Historically it has been made available in abundance, and often used in excess. With today’s increasing cost of energy, paper mills are demanding reduced operational costs to help with their competitiveness. Therefore, it makes sense to review air flow demands and, where suitable, apply old school thinking, i.e. nip-dewatering rather than felt dewatering.

ECOFLOW™

The primary function of a wire- and press section in a paper machine is to remove water from the paper sheet. In order to understand the effectiveness of individual elements (such as save-all pans and suction boxes) of a wire and press section, the dewatering rate must be measured. Without this, critical air flow (i.e. vacuum level) review and consequent optimization cannot be successfully carried out.

Water that is removed from the paper sheet contains air, and is often subject to foaming. Traditional magnetic liquid flow meters demand a homogenous flow and will not be able to provide accurate data. Ecoflow meters are designed to measure water flow across a mechanical restriction and are not sensitive to entrained air or foaming. These devices are used both under vacuum (in a separator drop leg) and in atmospheric conditions.


DOCTORING

The most economical method of water removal in a press section is nip dewatering, as opposed to felt dewatering which requires energy-demanding air flow. Nip dewatering is facilitated by allowing felts to run wet in combination with suitable doctoring and save-all equipment. Suction rolls are often equipped with double doctors to prevent re-wetting and maximise void volume to allow best water removal. Save-all pans should be designed to manage the water that is removed from the nips, and engineered to be rigid enough to accommodate doctor holders.


Dewatering and doctoring are not only related to energy consumption, but also plays a big role in paper machine runnability, efficiency and profitability, as well as paper profiles. Therefore, a well-designed and operated dewatering and doctoring system is the key to a well performing and energy efficient press section.


Runtech is one of the leading suppliers for the improved dewatering and doctoring solutions for the all kinds of pulp, paper, board and tissue machines. In many cases, Runtech’s solutions have led to a 1-3% increase in dryness after the press section which saves considerable energy in the dryer section (4-12% less steam).


EP TURBO BLOWERS

A vacuum is created as a result of moving air across a restriction. Fans, turbo blowers and liquid ring pumps can each be used to achieve this independently but are often used in combination with each other.

Turbo blowers have the benefit of being an inherently efficient way of compressing air for the modest compression ratios (less than 3,5) faced in a paper machine. A turbo blower is, for a given rotational speed and impeller design, a constant compression ratio device as opposed to a liquid ring pump which is a constant displacement machine. The power consumption of a turbo blower is a function of the air.


High speed motors, developmentdriven by frequency converters, allows a typical RunEco blower to provide paper machine vacuum levels between 30 and 70 kPa. A wider range of impeller designs allows highly efficient levels across the operating range. This means that the amount and the usage of throttling valves can be reduced to a minimum. The result is energy savings of 30 to 70% when compared with traditional vacuum systems.

furthermore, Ecopump turbo blowers operate without the need for sealant liquid (water), thus contributing to water savings in a paper mill.

VACUUM SYSTEM AND DEWATERING AUDITS

As is commonly known, vacuum demand varies with different paper grades, felts and machine speeds. A tailor-made solution with flexible and variable capacity can therefore balance the supply and demand, resulting in both optimised dewatering and minimised power consumption. For those reasons, Runtech performs professional vacuum system and dewatering audits prior to a rebuild project, for its customers.

Runtech engineers have done thousands of vacuum system audits and dewatering studies at paper mills over the last 20 years. Those studies and audits enables the company to benchmark the effectiveness of existing vacuum systems, dewatering equipment, suction elements, fabrics and felts. This information comes together in an often stepwise, rebuild and upgrade plan that results in minimised operational expense, coupled with a production increase and/or runnability improvements.


EP turbo blower

STORA ENSO SKOGHALL KM8, SWEDEN

Stora Enso Skoghall KM8 is the largest primary fibre board machine in Europe, with a width of 8.1 m and annual capacity of 450,000 tons. This machine produces predominantly liquid board for the food industry.

The vacuum system was upgraded in 2014. 10 liquid Ring Pumps were stopped and replaced by two (2) Ecopump turbo blowers and two (2) industrial fans. This allowed the mill to save 16.6 GWh/annum in direct electrical energy in addition to significant reductions in maintenance costs.


StoraEnso Skoghall KM8

LEIPA SCHWEDT PM4, GERMANY

Leipa Schwedt PM4 produces LWC paper. At 1600 m/min and 8100 mm trim width, it is a large machine. The machine was originally supplied with two (2) multistage turbo blowers and one (1) single stage blower. This system was rebuilt in August 2015 by replacing one of the multistage blowers with an Ecopump turbo blower, realising approx. 7 GWh/annum in reduced power consumption.


Leipa Schwedt PM4

CHINESE PAPER MILL (UNDISCLOSED NAME)

This customer purchased a RunEco system (Ecopump turbo blowers and Ecoflow™ devices) together with a new paper machine that produces 300,000 tons p.a. of fine paper. A traditional vacuum system for such a machine will typically result in a specific vacuum energy of 70-100 kWh/t. The supplied solution realised 50 kWh/t after startup in 2015. As a result of the subsequent customer care activities, the system was further optimised, thanks to the installed Ecoflow™ devices, and is now running at 35 kWh per ton of produced paper.


System Audit

IPET KAGIT, TURKEY

Ipek Kagit is a Turkish tissue paper producer. Runtech replaced the existing vacuum system (3 liquid ring pumps) of TM3 with a single Ecopump turbo blower in 2015. An EcoFlow™ system was installed at the same time allowing the mill to optimise the vacuum levels without sacrificing dewatering efficiency. The result was a 50% saving in energy, plus a significant reduction in water consumption.


Ipek Kagit TM3