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Gas valve auto­mat­i­cally opti­mises combus­tion

Vari­a­tions in the gas mixture no longer a problem


Although modern gas heating systems operate effi­ciently and ecolog­i­cally, new concepts are, never­the­less, called for in view of rising energy prices and more diverse raw mate­rial sources. For reasons of cost and to avoid short­ages, gas is now increas­ingly being obtained from new suppliers. This can result in fluc­tu­a­tions in the gas compo­si­tion, which in turn requires complex adjust­ment of the gas mixers to the partic­ular calorific values of the gas currently being supplied in the case of conven­tional gas heating systems. A new gas valve with stepper motor control and elec­tronic actu­a­tion now performs auto­matic adap­ta­tion to the quality of the gas. This permits rapid set-up of the heating system and at the same time avoids subse­quent extra costs resulting from changes in the gas quality.

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Figure 1: Link between gas and control system, the new gas valve F01

Simi­larly to a car engine, a heating system only provides optimum perfor­mance when oper­ating with a narrowly defined air-to-fuel ratio. In the case of natural gas, the so-called Lambda value (the gas-to-air ratio) is in the region of 1.3. The nitrogen content fluc­tu­ates consid­er­ably depending on the gas field and the amount of biogas fed in. Conven­tional mechan­ical mix regu­la­tors cannot provide compen­sa­tion for such fluc­tu­a­tions and so have to be re-adjusted. By contrast, the new gas valve F01 from ebm-papst Land­shut offers a conve­nient way of dealing with the problem of adjust­ment to different gas qual­i­ties: Elec­tronic control obvi­ates the need for manual setting. An ideal, econom­ical, and ecolog­ical combus­tion process is always guar­an­teed.

Natural gas from a variety of sources

As a result of liber­al­i­sa­tion of the gas market, gas compa­nies are now obliged to allow other suppliers to pump gas through their networks. Poten­tial short­ages are avoided by mixing gas from various fields or feeding in biogas. The calorific value of the resul­tant gas mix often fluc­tu­ates consid­er­ably despite the limit values agreed upon by the gas compa­nies. The conse­quence of this for the combus­tion process is that the amount of combus­tion air required has to be adjusted. In prac­tice, switching from high-calorific (so-called H gas) to low-calorific natural gas (L or even LL gas) for instance results in heat output losses of a double figure percentage magni­tude if the mixture ratio is not adapted accord­ingly.

This is also asso­ci­ated with an increase in the pollu­tant emis­sions of the heating system. A conven­tional gas and air modu­la­tion system with mechanical/pneumatic control is not able to accom­mo­date such fluc­tu­a­tions and manual adjust­ment is, there­fore, always neces­sary. By contrast, the new elec­tronic combus­tion control system provides constant auto­matic regu­la­tion by way of the gas valve (Fig. 1) to ensure optimum fuel util­i­sa­tion.

Modularer-Aufbau-o

Figure 2a and 2b: Modular Design: Safety module, stepper motor module and housing

Elec­tron­i­cally controlled

The micro­processor-controlled system regis­ters the combus­tion quality and ensures opti­mi­sa­tion regard­less of the instal­la­tion loca­tion and the amount of heat required. This is based on three impor­tant para­meters: Heat require­ment, air mass flow, and gas quality. The air mass flow is set on the basis of the amount of heat required, as it is propor­tional to the output. A mass flow meter inte­grated into the fan measures the air throughput. With stan­dard pre-mix burners, the compo­si­tion of the gas can easily be detected thanks to a partic­ular prop­erty of gases: Given iden­tical thermal load and excess air (same Lambda value), all the gases within one gas family exhibit iden­tical temper­a­tures at the burner.

This permits reli­able regu­la­tion of optimum combus­tion with a constant Lambda value as a func­tion of the temper­a­ture at the burner and the combus­tion air mass flow. Depending on the heating system concerned, the excess air can, thus, be kept constant over the entire heater modu­la­tion range. This does, however, presup­pose accu­rate and rapid regu­la­tion of the gas flow as spec­i­fied by the elec­tronics.

Gas valve as actu­ator

To be able to react accord­ingly to the infor­ma­tion received, the new gas valve F01 is equipped with a stepper motor. The deter­min­istic behav­iour of the motor – one pulse corre­sponds to one step – simpli­fies the control action with no detri­ment to accu­racy and safety. In prac­tice, the new valve permits a control ratio of 1:10 as opposed to the stan­dard 1:4 provided by pneu­matic modu­la­tion to date. The valve reli­ably regu­lates gas quan­ti­ties in the range between 1 and 40 kW rated output.

In extreme cases this control capacity makes it possible to reduce the heat output from 20 kW rated output to just 2 kW heat output for example if only minimal heating is required. Frequent burner start-up is, thus, avoided. Shorter shut­down times increase the effi­ciency of the heating system whilst at the same time reducing pollu­tant emis­sions.

The modular gas valve (Fig. 2a, 2b) combines proven safety tech­nology with a modern elec­tron­i­cally compat­ible actu­ator, the stepper motor with pres­sure regu­lator. The design is simple: Down­stream of the safety valve, the gas flows to the valve disc. This is precisely raised or lowered by the stepper motor as spec­i­fied by the control system, thus, accu­rately metering the flow of combus­tion gas. The new gas valve also simpli­fies the commis­sioning of gas heating systems.

Constant moni­toring and adjust­ment not only provide compen­sa­tion for fluc­tu­a­tions in the calorific value of the combus­tion gas. The system also auto­mat­i­cally senses the alti­tude of the instal­la­tion loca­tion and accord­ingly adjusts the quan­tity of gas and the combus­tion air flow required. There is then no need for time-consuming heating system setting work on site.

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