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....answers to some questions

Frequently Asked Questions (FAQs)

1. Is recirculating solvent fumes dangerous?

Recirculating solvent fumes is perfectly safe if designed and maintained correctly.

The solvent fumes are recirculated under carefully controlled conditions by the Optima controls with various safety functions. Each circuit of recirculation has a gas monitor to measure the solvent concentration as %LEL and this becomes the control point for the air recirculation. When the solvent levels are low, the recirculation is fully open reducing the exhaust to a minimum. However, as solvent levels increase then the recirculation damper will modulate increasing the exhaust and drawing in air make-up to dilute the solvent concentration and maintain constant safe levels.

optimal control panel EPM

An Optima control panel by EPM on a flexo press

The gas monitors incorporate various alarm safety functions should the solvent concentrations increase. First, it will close the recirculation totally with an audible/visual alarm and then shutdown the machine if levels continue to rise.

Additionally, depending on the dryers we can install flame arrestors which prevent a flash-back from a gas burner should the concentration get to an explosive condition.

Since the gas monitors are essential safety devices, they must be kept regularly calibrated every 3-6 months depending on the type. EPM Maintenance offer a planned calibration service and carry extensive spares. At the same time, we check the operation of all the alarm functions to ensure continuing safe operation.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

2. What does LEL mean ?

LEL means Lower Explosive Limit – it is a safety measure of solvent concentration and expressed as a %. In order for an explosion to take place, there must be a minimum concentration of fuel (i.e. solvent fume).

If we refer to 25% LEL, this means it is 25% of the concentration at which the mixture would explode (together with oxygen and a source of ignition). The LEL of Ethanol, for example, is 3.3%vol and therefore 0.8%vol equates to 25%LEL.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

5. Will optimising the dryers, affect the drying efficiency?

Recirculation itself does not affect drying efficiency. Although, 25%LEL appears to be a high concentration it is actually very low as %vol. It is the air that achieves the drying which, for example, might reduce from 99.6% to around 99.2%vol � the difference is negligible.

Solvent content in recirculated air is almost negligible.

As part of the optimising process, EPM rebalance the dryers which can make a significant improvement to the drying efficiency and speed. The dryer nozzles should be at a given distance from the web and set to the correct nozzle velocity � not too high or too low. Web speed sometimes can be increased by up to 15% simply by rebalancing the dryers.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

4. How much benefit will Optimisation provide me?

The improvement by dryer optimisation depends on many aspects, including:

  • Existing dryer design and set-up
  • Dryer heat source (gas, electric, thermal oil, etc) and energy cost
  • Production operating hours
  • Range of job types printed � width, substrate, speed, coat weight, solvents, etc
  • Type and design of abatement plant

EPM will be happy to survey your installation (free of charge) and advise you of the potential benefits with your particular installation.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

6. Will dryer optimisation reduce the emissions?

No, dryer optimisation does not reduce the total mass emission of VOC.

The exhaust airflow is reduced and the solvent concentration increased within safe limits however, the total mass emission actually remains the same. The purpose is to reduce the size of abatement plant and increase efficiency.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

3. Which type of LEL sensors are the best: IR or Catalytic?

The most common type of LEL sensors are infra-red (IR) and catalytic (often called cat�s) � both have their benefits.

IR sensors are around 4-6 times more expensive than catalytic but are more stable, last longer and less resistant to contamination.

The main drawback of IR is that they are very solvent-specific which is a problem where different solvents are used. Catalytic are much better at monitoring a range of solvents and are more commonly used on presses.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

7. Our presses have recirculation already included, what difference will it make?

Press manufacturers are increasingly designing recirculation already into the dryers. There are two methods of recirculating the dryer air � active and passive control.

Active control of recirculation varies the airflow for optimum conditions to maintain constant solvent levels. The exhaust is minimised and the solvent concentration is increased to the maximum safe operating limit. In this way, the load on the abatement plant is always minimised and ensures that the RTO is operating auto-thermally as much as possible.

Passive recirculation has fixed recirculation and exhaust with gas monitors to measure the LEL of the solvents which alarm and ultimately stop the machine. However, press dryers are normally set-up for the highest theoretical operating conditions with very high coverage at high speed � in reality, these conditions rarely occur. As a result, the production loading is significantly less than maximum. The result is larger abatement plant, higher running costs of abatement plant and reduced control of the recirculation in emergency conditions.

It is usually relatively easy to improve the efficiency of fixed passive recirculation by modifying the recirculation with active modulation of the recirculation to respond the production conditions.

A flexo press with fixed recirculation and LEL sensor for passive control

A flexo press with fixed recirculation and LEL sensor for passive control.

EPM can advise you if any further modification will be beneficial.

However, if the press recirculation is efficient, following the 3 steps towards compliance is still the best solution�

  • Step 1 � Install dampers and controls to divert the exhaust the air to atmosphere or abatement.
  • Step 2 – Monitoring the emissions profile
  • Step 3 � design and install abatement

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

8. What ongoing maintenance will there be?

Ongoing maintenance of the optimisation system is minimal.

The solvent gas monitors will require routine calibration normally every 3 months since they are an essential safety and control device. EPM Maintenance offer an extensive calibration service and hold a large stock of spares. At the same time, we check the operation of all the alarm functions to ensure continuing safe operation.

Calibrating a catalytic LEL sensor

Calibrating a catalytic LEL sensor.

The operation of dampers is constantly being monitored and so do not need routine maintenance. If flame arrestors are fitted, they will need to be removed and cleaned usually annually.

The abatement plant will require annual maintenance and emissions monitoring.

EPM Consultancy have MCerts certification and offer annual emissions monitoring of VOC, CO & NOx.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

10. What happens to the optimisation system in a power failure?

Every aspect of the Optima installation by EPM is designed to be as safe and reliable as possible.

However, if the power fails to the system all dampers have mechanical springs to quickly default them to safe positions. This includes immediately closing the recirculation and diverting the exhaust to atmosphere. Additionally, the control panel would stop the press as an additional safety action.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

12. What is the best abatement technology?

The technology should be designed specifically for a specific process. This will depend on the criteria of the application, i.e. production hours, airflow, levels of solvent concentration, etc.

However, for most flexible packaging, printing and coating processes the most cost-effective solution would be a Regenerative Thermal Oxidiser (RTO) giving good energy efficiency, effective VOC reduction, low maintenance and at reasonable cost.

EPM Consultancy can help you select the best technology and design for your particular circumstances.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

14. How do I ensure the RTO is operating efficiently?

As part of the acceptance, EPM will test the RTO for optimum operating efficiency. Operating Permits specify that an RTO should have the correlation between temperature and emissions determined so that the temperature control point is high enough but not too high as to use unnecessary energy.

The Operating Permit will stipulate the emissions from an RTO should be monitored every 12 months. EPM Consultancy has MCerts certification and offer annual emissions monitoring of VOC, CO & NOx.

Emissions Monitoring of an RTO by EPM.

Emissions Monitoring of an RTO by EPM.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

9. What do the operators have to do?

Nothing � everything in the Optima system is automatic and self-checking.

We provide training to the Operators simply for awareness and understanding of the system operation.

An Operator checking the optimisation on a Cerutti gravure

An Operator checking the optimisation on a Cerutti gravure.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

11. What happens in the event of an emergency on the press?

The Optima control system continuously monitors the press emergency stop, web break and fire alarm circuits (where fitted) in fail-safe mode.

In the event of an alarm, the Optima system immediately revert all dampers to their safe default positions. This includes immediately closing the recirculation and diverting the exhaust to atmosphere.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

13. Could we use the waste heat from an RTO?

RTO�s are designed to be energy-efficient within themselves. Although the combustion temperature typically is around 800-850oC, the highly efficient heat recovery by the ceramic media means that only low-grade heat being emitted at around 100oC is normally available. This heat can be used for example via a heat exchanger for simple heating to warehouses and storage areas.

If levels of solvent are consistently high (typically above 2.5 g/m3) then the burner in the RTO would switch off in order to maintain the desired operating temperature, i.e. the unit becomes autothermal or self-sustaining. As the solvent levels increase (e.g. >4-5 g/m3) then excess heat is generated which usually is released from the combustion chamber directly to the stack via a high solvent bypass without recovering the heat, again to maintain the combustion temperature set point. If this situation occurs regularly, the high grade heat can be used for heat recovery for example to thermal oil.

Thermal oil heat recovery in a high temperature bypass of an RTO

The loading must however be assessed carefully to ensure that only excess heat is used. If not, then the RTO burner can be used as a primary heat source which is not energy-efficient.

The Carbon Trust could support such installations with interest-free loans – EPM Consultancy are registered with the carbon Trust and can assess the viability of various options for you.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

15. I have an RTO which is proving expensive to run - what can I do?

This could be due to a variety of reasons, including:

  • Inefficient machine dryer operation or adjustment
  • Diverting dampers not operating correctly leaking �fresh air� into the RTO
  • Diverting dampers operating with the wrong machine run signal exhausting �fresh air� unnecessarily to the RTO
  • Process changes away from original design
  • Poor design or operation of the RTO i.e. inefficient heat exchange media

EPM Maintenance would be happy to survey and modify any inefficient installation – the initial assessment survey being free of charge.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

16. Will we need a fixed VOC monitoring system on my abatement plant?

Ultimately, this will depend on the requirements of your Local Authority. Large oxidiser installations often are required to have fixed FID monitoring (i.e. CEMS Continuous Emissions Monitoring System) but there is no definition of large.

Smaller oxidiser installations can be surrogate monitored by oxidisation temperature. This is allowed because oxidisation temperature directly affects VOC emissions higher temperature improves oxidisation and reduces VOC emissions. The relationship between temperature is correlated during abatement commissioning and acceptance trials to determine the control set point and low temperature alarms. The temperature can then be satisfactorily recorded as a surrogate of VOC emissions.

If you would like to discuss any aspect of the information outlined in this question, please contact EPM at contact@epm.uk.com.

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