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VOC Emissions from Manufacturing Processes

4. VOC Reduction, Step by Step

4.1 Introduction

This chapter presents a practical and effective method to reduce emissions of VOCs to the atmosphere.

Every company is different from other companies, and the described method should be regarded as a guideline that can be modified according to the nature and needs of each company.

The reduction of VOC serves two main purposes:

1.	To comply with present and future regulation (see chapter 2) regarding: emission concentrations immission contribution
2.	To reduce the impact on the environment to the extent possible with regard to technical and economical possibilities.

The last purpose can be expressed by means of an Environmental Performance Indicator (EPI). Such an indicator could be based upon the quantity of emitted solvents per year, in relation to the toxicity of the components (i.e. calculated as the C_r-value (DEPA, guideline no. 9, 1992) and the production volume. The EPI value will be a natural control parameter in an environmental management system, i.e. ISO 14001.

The above is illustrated graphically in Figure 4.1, also containing an example of an EPI.

Figure 4.1
Purposes of VOC reduction.

The EPI will require measurements of VOC concentrations but only in the beginning. Afterwards simulations by spreadsheets can be used and only very few measurements are needed.

The C_r-value is a theoretical value to be used only in cases with toxicological substances (not odour-related) with the same effect.

Activities to fulfil above purposes cannot and should not be handled separately but should be regarded as an integrated process. In practice, this means that intermediate reduction methods always should fit into an overall program for fulfilling future reduction goals. This will be illustrated in the next chapter.

4.2 General methodology

Methods for reduction of VOC emissions

Methods for reduction of VOC can be grouped into two categories:

1. Cleaner technology methods (reduction at the source), including substitution
2. Traditional methods (end of pipe solutions), i.e. incineration

Ideally, all reductions should be managed by means of cleaner technology methods or by means of Best Available Technology (BAT). Practise has however shown that in general it is not possible to use only such methods to obtain compliance with rules and guidelines. This is especially the case in relation to older existing plants.

Practise has also shown that using cleaner technology methods before having a total view of the future reduction needs can lead to a substantial increase in the total investment and operation cost for the emission reduction system.

An example is reduction of the concentration of VOC in certain outlets, which are later being combined with other outlets to be cleaned by an incineration plant and where fuel is necessary to maintain the proper incineration temperature. In such a case, it would had been better both from an economic - and also often from an environmental viewpoint to maintain the high VOC concentration and thus reduce (or avoid) the use of e.g. natural gas to obtain the demanded incineration temperature.

This example illustrates the very importance of having a total view of the whole situation before deciding what methods to use for the reduction of VOCs.

Methodology in emission reduction

The recommended methodology in emission reduction is:

The method is illustrated graphically in

Figure 4.2.

In chapter 4.3 each of the activities 1-6 are described in detail.

Figure 4.2
General methodology in emission reduction.

4.3 Detailed methodology

In the following, each of the activities mentioned in chapter 4.2 and the corresponding

Figure 4.2 are described in detail.

Purpose

4.3.1 Detailed survey of emissions from all sources

This is the most important activity as it gives the whole foundation for all future activities. The work is time-consuming, but it is very important to understand that only a detailed knowledge of the emissions and the relations to the production can give the background for optimum reduction activities (effectiveness, costs, and future production flexibility).

Listing of all emission sources

This listing should not only include the stacks but also the separate pipes connected to the stacks. All sources including major sources, minor sources and room ventilation (with solvent vapours) should be listed. It is very important to have this listing of sources on a detailed level, as present combination of sources, pipes and stacks is not always based upon optimum considerations concerning environment. This system is illustrated in Figure 4.3, where the pipes are numbered by process and pipe No. 1.1 … Nn.

Figure 4.3
System to list stacks, pipes and processes.

Emissions must be correlated to the production that takes place:

	Processes
	Production (receipt)
	Production volume (rate)
	Other relevant production data

Some production scenarios will result in low emissions, other in high emissions. Data on emission measurements should always be registered together with production data.

For each of the processes Process 1 …. Process N in Figure 4.3, emission measurements should be taken for all types of production (receipts) taking place in the company. If the number of receipts is high, the number of measurements can be reduced by interpolation between measurements as follows:

If interpolation is used, it is recommended that the difference between the lowest and highest emission does not exceed a factor 2. If this not is the case, the number of measurements must be increased. Interpolation between different measurements can be done on basis of vapour pressure.

Emission measurements

As the emission varies during the time of production, it is important that the emission measurements are performed continuously over the production period. This can be obtained by taking a high number of samples on activated carbon tubes. This method is both very time-consuming and very expensive.

A better, easier and more economical method is to use TOC (Total Organic Carbon) measurements by use of a portable FID (Flame Ionisation Detector).

It is a practical experience, that TOC measurements are more reliable than measurements of VOC (by use of carbon tubes). The emission values can easily be calculated into VOC concentrations by knowledge of the mixture of the solvents. Use of TOC measurements are especially of high value for emissions varying with time, which is the case for the processes dealt with in this report.

Based upon the TOC measurements, calibration data, and knowledge on the composition of the solvents in the actual process (the distribution of the different solvents), it is possible to calculate the actual concentration in the gas in mg VOC/m³. (The detailed calculation method is not described in the present text – but can in most cases be found in the manual of the measuring instrument).

Data can be registered in a spreadsheet as shown in Table 4.1 and Table 4.2. When all data have been collected, it is possible to simulate different production scenarios, i.e. different combinations of processes and receipts. By using the "SORT" and "SUM" functions in the spreadsheet, the emissions from the different processes and stacks can be separated.

Such scenarios should be performed for several (realistic) combinations of processes, receipts and time-relation.

In Table 4.1 and Table 4.2 simple examples are given on a scenario sorted by process ( Table 4.1) and by stacks (Table4.2).

Table 4.1 is a spreadsheet which can be sorted in different ways. The spreadsheet gives detailed information for all streams for specific processes, i.e. combination of process, receipt, pipe and stack. (More pipes to one stack). The emissions for each separate pipe are given on concentration basis and on emission basis, both related to time (i.e. exceeding 8 hours). The spreadsheet gives a good overview of the emission situation. It will for example be possible to access whether or not it can be a good idea to combine the separate pipes to other stacks (i.e. to collect high concentrations to an incineration unit and low concentrations to a direct outlet).

Table 4.1 Look here!
Example of scenario with 3 processes sorted by processes. (Concentration values are not shown.)

Table 4.2 Look here!
Example of scenario with 3 processes sorted by stacks. (Concentration values are not shown)

4.3.2 Control of compliance with present and future limit values

Purpose

The purpose of this activity is to control compliance with existing rules and guidelines and with conditions in environmental permits.

Activities

Control of compliance is made on basis of the emission scenarios. Emission scenarios can be chosen among the scenarios performed in chapter 4.3.1.

The emission scenarios used for control should be the scenarios with the highest emissions and lowest C_r-values estimated by the factor [Emission g/sec.]/[C_r-value]. The scenario with the highest value is the most critical scenario.

The emission is the total emission from all processes and stacks, and the C_r-value is the total value calculated on basis of the formula in DEPA guideline no. 9, 1992.

Compliance with emission concentrations

Control of compliance is performed in accordance with DEPA guideline no. 9, 1992. The mass flow is determined as the [Total flow in kg/working shift]/ [Number of hours in working shift] before cleaning (incineration etc.). The mass flow is easily calculated by use of the emission spreadsheet.

If the mass flow is above the limit given in DEPA guideline no. 9, 1992, all emission concentrations should be below the emission limit for the different classes of organic solvents.

This is controlled on basis of the emission spreadsheet where it is possible to calculate the hourly mean value of the concentrations in the different stacks for the relevant production scenarios.

Compliance with immission contribution limits

Control of compliance with the limits for the immission contribution values (C_r-values, DEPA guideline no. 9, 1992) can be performed either on basis of the mean emission values from the stacks or on basis of a period with maximum values. Both set of values are easily obtained from the emission spreadsheet.

The calculation of the immission contribution should be performed by use of the OML model – multi source version (available at the National Environmental Research Institute – Danmarks Miljøundersøgelser (DMU)). The necessary source data are shown in Table 4.3.

Table 4.3
OML-source data.

Evaluation of results

If the results of the emission and immission compliance control are that the company does not comply with the limit values, work should be initiated to reduce emissions and/or to modify stack heights to obtain compliance.

If the results of the emission and immission compliance control are that the company is in compliance with the limit values, work should be initiated to continuously improve the environmental performance indicator for VOC (see chapter 4.1, Figure 4.1 and chapter 4.3.5).

4.3.3 Setting up of different reduction scenarios

Purpose

The purpose of this activity is to give the best background for choosing the best combination of reduction methods.

Activities

If the company not is in compliance with the limit values for VOCs, the procedure is as shown in Figure 4.4

Figure 4.4
The procedure when the company is not in compliance with the limit values.

Only scenarios capable of fulfilling compliance should be regarded. In finding the best solutions, it is often advisable to review the different streams (pipes) of VOC flows and to assess if other combinations of pipes and stacks would be more relevant. This is specially the case when incineration is necessary. Here it is of utmost importance to obtain as high concentrations as possible to reduce the need for supply energy (for example natural gas).

If the company already is in compliance, it should look upon how to reduce the impact on the environment by reducing the value of relevant EPI. This is illustrated in Figure 4.1, where the dynamic relationship between the different parameters in the EPI formula, the reduction possibilities and the corresponding action plans are shown.

The illustrated EPI should only be regarded as an example.

For use of action plans, please refer to chapter 4.3.5 and for reporting of EPI chapter 4.3.4.

Figure 4.5
From EPI to action plans.

4.3.4 Choosing the best reduction scenario

Purpose

In general, there is no specific method to choose the best combination of methods for VOC reduction, but some general advice can be given.

Activities

The different scenarios are compared by a number of parameters regarding reduction efficiency, costs, production related parameters etc.

The different scenarios can be compared as illustrated in Table 4.4.

The parameters used are only examples. Choosing of scenario can be made on basis of the parameters and the importance of each parameter for the company. Common sense and knowledge of present and future needs for the company should be used in this process.

Table 4.4
Parameters to compare different scenarios for emission reduction.

4.3.5 Action plans

Purpose

The purpose of the action plans is:

	To define tasks, time schedule and persons responsible for carrying out the plans
	To inform other involved persons in the company of ongoing and coming activities
	To inform the authorities of ongoing and coming activities
	To report on finished, ongoing and coming activities

The action plans should be available to all relevant persons inside and outside the company.

Activities

Action plans are based upon the results of the activities described in chapter 4.3.4.

Action plans are best organised on a pyramidal structure as shown in Figure 4.6.

Figure 4.6
Action plan structure.

A dynamic concept for the design of action plans is shown in Table 4.5.

Table 4.5 Look here!
Example of design of action plan

4.4 Reporting on activities and EPI values

Purpose

The purpose of this activity is to report on finished, ongoing and coming activities and related results with regard to the impact on the environment.

Activities

Different reporting activities can be relevant:

The reporting activities 2, 3 and 4 can be combined with the action plans to show the effect of the action plans. For the reporting activity 4 this could be illustrated graphically as in Figure 4.7.

Figure 4.7
Reporting of results of action plans by use of EPI.

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